diff --git a/multisig/src/storage.rs b/multisig/src/storage.rs
new file mode 100644
index 0000000..e8de6be
--- /dev/null
+++ b/multisig/src/storage.rs
@@ -0,0 +1,42 @@
+use soroban_sdk::{Address, Env, Vec};
+
+use crate::types::DataKey;
+
+// Signers (issue #101): dedicated persistent entries plus an O(1) membership
+// map, instead of a `Signers` list loaded in full from instance storage on
+// every invocation and checked with `Vec::contains`.
+
+pub fn is_signer(env: &Env, signer: &Address) -> bool {
+    env.storage()
+        .persistent()
+        .get(&DataKey::IsSigner(signer.clone()))
+        .unwrap_or(false)
+}
+
+pub fn signer_list(env: &Env) -> Vec<Address> {
+    env.storage()
+        .persistent()
+        .get(&DataKey::Signers)
+        .unwrap_or(Vec::new(env))
+}
+
+pub fn add_signer(env: &Env, signer: &Address) {
+    env.storage()
+        .persistent()
+        .set(&DataKey::IsSigner(signer.clone()), &true);
+    let mut list = signer_list(env);
+    list.push_back(signer.clone());
+    env.storage().persistent().set(&DataKey::Signers, &list);
+}
+
+pub fn remove_signer(env: &Env, signer: &Address) {
+    env.storage()
+        .persistent()
+        .remove(&DataKey::IsSigner(signer.clone()));
+    let list = signer_list(env);
+    if let Some(idx) = list.iter().position(|s| &s == signer) {
+        let mut list = list;
+        list.remove(idx as u32);
+        env.storage().persistent().set(&DataKey::Signers, &list);
+    }
+}
diff --git a/multisig/src/storage_test.rs b/multisig/src/storage_test.rs
new file mode 100644
index 0000000..0fb099d
--- /dev/null
+++ b/multisig/src/storage_test.rs
@@ -0,0 +1,44 @@
+use soroban_sdk::{contract, testutils::Address as _, Address, Env};
+
+use crate::storage;
+
+// Dummy contract purely to give these storage-layer unit tests a contract
+// context (issue #101 only touches storage/types here).
+#[contract]
+struct Dummy;
+
+fn setup() -> (Env, Address) {
+    let env = Env::default();
+    let id = env.register_contract(None, Dummy);
+    (env, id)
+}
+
+#[test]
+fn is_signer_is_o1_membership() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let signer = Address::generate(&env);
+        assert!(!storage::is_signer(&env, &signer));
+        storage::add_signer(&env, &signer);
+        assert!(storage::is_signer(&env, &signer));
+        storage::remove_signer(&env, &signer);
+        assert!(!storage::is_signer(&env, &signer));
+    });
+}
+
+#[test]
+fn signer_list_enumerates_added_signers() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let a = Address::generate(&env);
+        let b = Address::generate(&env);
+        storage::add_signer(&env, &a);
+        storage::add_signer(&env, &b);
+        assert_eq!(storage::signer_list(&env).len(), 2);
+
+        storage::remove_signer(&env, &a);
+        let remaining = storage::signer_list(&env);
+        assert_eq!(remaining.len(), 1);
+        assert_eq!(remaining.get(0), Some(b));
+    });
+}
diff --git a/multisig/src/types.rs b/multisig/src/types.rs
index 32a5af4..3ba0d1e 100644
--- a/multisig/src/types.rs
+++ b/multisig/src/types.rs
@@ -3,6 +3,13 @@ use soroban_sdk::{contracttype, Address, BytesN, Symbol, Val, Vec};
 #[contracttype]
 #[derive(Clone)]
 pub enum DataKey {
+use soroban_sdk::{contracttype, Address, BytesN, Symbol, Val, Vec};
+
+#[contracttype]
+#[derive(Clone)]
+pub enum DataKey {
+    /// O(1) membership check — see issue #101.
+    IsSigner(Address),
     /// Map<Address, u32>: every signer and their voting weight.
     Signers,
     /// Approval weight an action needs for `is_approved`.
diff --git a/options_market/src/lib.rs b/options_market/src/lib.rs
index e69de29..4cfaf0b 100644
--- a/options_market/src/lib.rs
+++ b/options_market/src/lib.rs
@@ -0,0 +1,7 @@
+#![no_std]
+
+mod storage;
+mod types;
+
+#[cfg(test)]
+mod test;
diff --git a/options_market/src/storage.rs b/options_market/src/storage.rs
index e69de29..a13099a 100644
--- a/options_market/src/storage.rs
+++ b/options_market/src/storage.rs
@@ -0,0 +1,98 @@
+use soroban_sdk::{Address, Env, Vec};
+
+use crate::types::{Config, DataKey, OptionPosition, Stats, POSITIONS_PER_PAGE};
+
+// ─── Config / Stats (issue #102) ───────────────────────────────────────────
+
+pub fn load_config(env: &Env) -> Config {
+    env.storage().instance().get(&DataKey::Config).unwrap()
+}
+
+pub fn save_config(env: &Env, config: &Config) {
+    env.storage().instance().set(&DataKey::Config, config);
+}
+
+pub fn load_stats(env: &Env) -> Stats {
+    env.storage()
+        .instance()
+        .get(&DataKey::Stats)
+        .unwrap_or(Stats {
+            premiums_collected: 0,
+            open_interest: 0,
+            premium_pool: 0,
+            series_count: 0,
+            position_counter: 0,
+        })
+}
+
+pub fn save_stats(env: &Env, stats: &Stats) {
+    env.storage().instance().set(&DataKey::Stats, stats);
+}
+
+// ─── Positions (issue #103) ────────────────────────────────────────────────
+
+pub fn load_position(env: &Env, position_id: u64) -> Option<OptionPosition> {
+    env.storage()
+        .persistent()
+        .get(&DataKey::Position(position_id))
+}
+
+pub fn save_position(env: &Env, position_id: u64, position: &OptionPosition) {
+    env.storage()
+        .persistent()
+        .set(&DataKey::Position(position_id), position);
+}
+
+// ─── Paginated user position index (issue #100) ────────────────────────────
+//
+// Ids are appended to fixed-size pages (`POSITIONS_PER_PAGE` per page)
+// instead of one ever-growing `Vec<u64>`. Each page is its own persistent
+// entry, so a single trade only reads and rewrites the current page rather
+// than the user's whole history — bounded write bytes no matter how many
+// positions the user has opened.
+
+pub fn user_position_count(env: &Env, user: &Address) -> u32 {
+    env.storage()
+        .persistent()
+        .get(&DataKey::UserPositionCount(user.clone()))
+        .unwrap_or(0)
+}
+
+fn load_page(env: &Env, user: &Address, page: u32) -> Vec<u64> {
+    env.storage()
+        .persistent()
+        .get(&DataKey::UserPositionPage(user.clone(), page))
+        .unwrap_or(Vec::new(env))
+}
+
+/// O(1) append: only the current (partially-filled) page is read and
+/// rewritten; earlier pages are untouched.
+pub fn add_user_position(env: &Env, user: &Address, position_id: u64) {
+    let count = user_position_count(env, user);
+    let page_index = count / POSITIONS_PER_PAGE;
+    let mut page = load_page(env, user, page_index);
+    page.push_back(position_id);
+    env.storage()
+        .persistent()
+        .set(&DataKey::UserPositionPage(user.clone(), page_index), &page);
+    env.storage()
+        .persistent()
+        .set(&DataKey::UserPositionCount(user.clone()), &(count + 1));
+}
+
+/// Returns up to `limit` position ids starting at `cursor` (an index into
+/// the user's full history, oldest first).
+pub fn get_user_positions_page(env: &Env, user: &Address, cursor: u32, limit: u32) -> Vec<u64> {
+    let total = user_position_count(env, user);
+    let mut out = Vec::new(env);
+    let mut i = cursor;
+    let end = total.min(cursor.saturating_add(limit));
+    while i < end {
+        let page = load_page(env, user, i / POSITIONS_PER_PAGE);
+        if let Some(id) = page.get(i % POSITIONS_PER_PAGE) {
+            out.push_back(id);
+        }
+        i += 1;
+    }
+    out
+}
diff --git a/options_market/src/test.rs b/options_market/src/test.rs
index e69de29..1341eee 100644
--- a/options_market/src/test.rs
+++ b/options_market/src/test.rs
@@ -0,0 +1,111 @@
+use soroban_sdk::{contract, testutils::Address as _, Address, Env};
+
+use crate::storage;
+use crate::types::{Config, OptionPosition, PositionStatus, Stats};
+
+// A dummy contract purely so these storage-layer unit tests have a contract
+// context to run `env.storage()` calls against (issues #100/#102/#103 only
+// touch storage/types — there is no `#[contract]` in this crate to attach
+// entrypoints to yet).
+#[contract]
+struct Dummy;
+
+fn setup() -> (Env, Address) {
+    let env = Env::default();
+    let id = env.register_contract(None, Dummy);
+    (env, id)
+}
+
+#[test]
+fn config_round_trips() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let config = Config {
+            admin: Address::generate(&env),
+            oracle: Address::generate(&env),
+            token: Address::generate(&env),
+            fee_recipient: Address::generate(&env),
+            fee_bps: 50,
+            paused: false,
+        };
+        storage::save_config(&env, &config);
+        let loaded = storage::load_config(&env);
+        assert_eq!(loaded.fee_bps, 50);
+        assert!(!loaded.paused);
+    });
+}
+
+#[test]
+fn stats_defaults_to_zero_then_round_trips() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let stats = storage::load_stats(&env);
+        assert_eq!(stats.position_counter, 0);
+
+        let updated = Stats {
+            premiums_collected: 100,
+            open_interest: 5,
+            premium_pool: 100,
+            series_count: 1,
+            position_counter: 1,
+        };
+        storage::save_stats(&env, &updated);
+        assert_eq!(storage::load_stats(&env).position_counter, 1);
+    });
+}
+
+#[test]
+fn position_status_replaces_the_two_bool_flags() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let owner = Address::generate(&env);
+        let position = OptionPosition {
+            series_id: 1,
+            owner: owner.clone(),
+            side_is_buyer: true,
+            amount: 10,
+            collateral_locked: 0,
+            status: PositionStatus::Open,
+            opened_at: env.ledger().timestamp(),
+        };
+        storage::save_position(&env, 1, &position);
+        let loaded = storage::load_position(&env, 1).unwrap();
+        assert_eq!(loaded.status, PositionStatus::Open);
+
+        let exercised = OptionPosition {
+            status: PositionStatus::Exercised,
+            ..loaded
+        };
+        storage::save_position(&env, 1, &exercised);
+        assert_eq!(
+            storage::load_position(&env, 1).unwrap().status,
+            PositionStatus::Exercised
+        );
+    });
+}
+
+#[test]
+fn user_positions_append_in_o1_and_paginate() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let user = Address::generate(&env);
+        for i in 0..150u64 {
+            storage::add_user_position(&env, &user, i);
+        }
+        assert_eq!(storage::user_position_count(&env, &user), 150);
+
+        let page = storage::get_user_positions_page(&env, &user, 0, 10);
+        assert_eq!(page.len(), 10);
+        assert_eq!(page.get(0), Some(0));
+
+        // Crosses a page boundary (POSITIONS_PER_PAGE == 64).
+        let page = storage::get_user_positions_page(&env, &user, 60, 10);
+        assert_eq!(page.len(), 10);
+        assert_eq!(page.get(0), Some(60));
+        assert_eq!(page.get(9), Some(69));
+
+        // Past the end.
+        let page = storage::get_user_positions_page(&env, &user, 145, 10);
+        assert_eq!(page.len(), 5);
+    });
+}
diff --git a/options_market/src/types.rs b/options_market/src/types.rs
index e69de29..f4e420a 100644
--- a/options_market/src/types.rs
+++ b/options_market/src/types.rs
@@ -0,0 +1,69 @@
+use soroban_sdk::{contracttype, Address};
+
+/// Consolidated hot configuration, loaded once per call instead of five
+/// separate instance reads (CollateralToken, FeeRecipient, FeeRateBps,
+/// PremiumPool, TotalPremiumsCollected). See issue #102.
+#[contracttype]
+#[derive(Clone)]
+pub struct Config {
+    pub admin: Address,
+    pub oracle: Address,
+    pub token: Address,
+    pub fee_recipient: Address,
+    pub fee_bps: u32,
+    pub paused: bool,
+}
+
+/// Aggregated counters, written once per call instead of several
+/// read-modify-write single-counter entries. See issue #102.
+#[contracttype]
+#[derive(Clone)]
+pub struct Stats {
+    pub premiums_collected: i128,
+    pub open_interest: i128,
+    pub premium_pool: i128,
+    pub series_count: u64,
+    pub position_counter: u64,
+}
+
+/// `Open`/`Exercised`/`Settled`/`Refunded` replaces the two `bool` flags
+/// (`is_exercised`, `is_settled`) that used to live directly on
+/// `OptionPosition`. See issue #103.
+#[contracttype]
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum PositionStatus {
+    Open,
+    Exercised,
+    Settled,
+    Refunded,
+}
+
+/// Compact position layout (issue #103): the boolean flags are folded into
+/// `status`, and the struct only carries the fields every reader needs.
+/// `opened_at` is a cold field kept here rather than split into a second
+/// entry — splitting it out is left for a follow-up once it's clear readers
+/// need `OptionPosition` without paying for it.
+#[contracttype]
+#[derive(Clone)]
+pub struct OptionPosition {
+    pub series_id: u64,
+    pub owner: Address,
+    pub side_is_buyer: bool,
+    pub amount: i128,
+    pub collateral_locked: i128,
+    pub status: PositionStatus,
+    pub opened_at: u64,
+}
+
+#[contracttype]
+#[derive(Clone)]
+pub enum DataKey {
+    Config,
+    Stats,
+    Position(u64),
+    UserPositionCount(Address),
+    UserPositionPage(Address, u32),
+}
+
+/// Number of position ids stored per `UserPositionPage` bucket (issue #100).
+pub const POSITIONS_PER_PAGE: u32 = 64;
diff --git a/price_oracle/src/lib.rs b/price_oracle/src/lib.rs
index e69de29..3c1f7e4 100644
--- a/price_oracle/src/lib.rs
+++ b/price_oracle/src/lib.rs
@@ -0,0 +1,7 @@
+#![no_std]
+
+mod storage;
+mod types;
+
+#[cfg(test)]
+mod storage_test;
diff --git a/price_oracle/src/storage.rs b/price_oracle/src/storage.rs
new file mode 100644
index 0000000..c86b73a
--- /dev/null
+++ b/price_oracle/src/storage.rs
@@ -0,0 +1,43 @@
+use soroban_sdk::{Address, Env, Vec};
+
+use crate::types::DataKey;
+
+// Feeders (issue #101): moved out of instance storage — which is loaded in
+// full on every invocation, including the hot `report_price`/`get_price`
+// paths — into dedicated persistent entries, with an O(1) membership map
+// instead of `Vec::contains`.
+
+pub fn is_feeder(env: &Env, feeder: &Address) -> bool {
+    env.storage()
+        .persistent()
+        .get(&DataKey::IsFeeder(feeder.clone()))
+        .unwrap_or(false)
+}
+
+pub fn feeder_list(env: &Env) -> Vec<Address> {
+    env.storage()
+        .persistent()
+        .get(&DataKey::Feeders)
+        .unwrap_or(Vec::new(env))
+}
+
+pub fn add_feeder(env: &Env, feeder: &Address) {
+    env.storage()
+        .persistent()
+        .set(&DataKey::IsFeeder(feeder.clone()), &true);
+    let mut list = feeder_list(env);
+    list.push_back(feeder.clone());
+    env.storage().persistent().set(&DataKey::Feeders, &list);
+}
+
+pub fn remove_feeder(env: &Env, feeder: &Address) {
+    env.storage()
+        .persistent()
+        .remove(&DataKey::IsFeeder(feeder.clone()));
+    let list = feeder_list(env);
+    if let Some(idx) = list.iter().position(|f| &f == feeder) {
+        let mut list = list;
+        list.remove(idx as u32);
+        env.storage().persistent().set(&DataKey::Feeders, &list);
+    }
+}
diff --git a/price_oracle/src/storage_test.rs b/price_oracle/src/storage_test.rs
new file mode 100644
index 0000000..3287ddc
--- /dev/null
+++ b/price_oracle/src/storage_test.rs
@@ -0,0 +1,44 @@
+use soroban_sdk::{contract, testutils::Address as _, Address, Env};
+
+use crate::storage;
+
+// Dummy contract purely to give these storage-layer unit tests a contract
+// context (issue #101 only touches storage/types here).
+#[contract]
+struct Dummy;
+
+fn setup() -> (Env, Address) {
+    let env = Env::default();
+    let id = env.register_contract(None, Dummy);
+    (env, id)
+}
+
+#[test]
+fn is_feeder_is_o1_membership() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let feeder = Address::generate(&env);
+        assert!(!storage::is_feeder(&env, &feeder));
+        storage::add_feeder(&env, &feeder);
+        assert!(storage::is_feeder(&env, &feeder));
+        storage::remove_feeder(&env, &feeder);
+        assert!(!storage::is_feeder(&env, &feeder));
+    });
+}
+
+#[test]
+fn feeder_list_enumerates_added_feeders() {
+    let (env, id) = setup();
+    env.as_contract(&id, || {
+        let a = Address::generate(&env);
+        let b = Address::generate(&env);
+        storage::add_feeder(&env, &a);
+        storage::add_feeder(&env, &b);
+        assert_eq!(storage::feeder_list(&env).len(), 2);
+
+        storage::remove_feeder(&env, &a);
+        let remaining = storage::feeder_list(&env);
+        assert_eq!(remaining.len(), 1);
+        assert_eq!(remaining.get(0), Some(b));
+    });
+}
diff --git a/price_oracle/src/types.rs b/price_oracle/src/types.rs
index 74bcf5c..476d0e1 100644
--- a/price_oracle/src/types.rs
+++ b/price_oracle/src/types.rs
@@ -10,6 +10,10 @@ pub enum DataKey {
     /// before it returns an aggregate at all. Defaults to 1 at initialize
     /// (the original behavior: any single fresh report is enough).
     MinReports,
+    /// O(1) membership check — see issue #101. `Feeders` below stays around
+    /// only for enumeration (e.g. `get_feeders`), and now lives in
+    /// persistent storage instead of instance storage.
+    IsFeeder(Address),
     Feeders,
     PriceReport(Symbol, Address),
     AggregatedPrice(Symbol),