diff --git a/apps/contracts/energy_token/src/lib.rs b/apps/contracts/energy_token/src/lib.rs
index 40f2f61..12522b6 100644
--- a/apps/contracts/energy_token/src/lib.rs
+++ b/apps/contracts/energy_token/src/lib.rs
@@ -816,3 +816,6 @@ mod tests {
         client.retire(&user, &String::from_str(&env, "empty"));
     }
 }
+
+#[cfg(test)]
+mod overflow_tests;
\ No newline at end of file
diff --git a/apps/contracts/energy_token/src/overflow_tests.rs b/apps/contracts/energy_token/src/overflow_tests.rs
new file mode 100644
index 0000000..056301b
--- /dev/null
+++ b/apps/contracts/energy_token/src/overflow_tests.rs
@@ -0,0 +1,186 @@
+//! Overflow/underflow test coverage for energy_token arithmetic (#559).
+//!
+//! Tests every arithmetic path that involves i128 addition or subtraction:
+//! - mint(): balance overflow, total_minted overflow
+//! - transfer(): recipient balance overflow, sender underflow
+//! - burn(): underflow (burn more than balance)
+//! - burn_from(): underflow, insufficient allowance
+//! - transfer_from(): recipient balance overflow
+//! - approve(): negative amount rejected
+//! - zero-amount rejections (positive-only guard)
+
+#![cfg(test)]
+
+use energy_token::{EnergyToken, EnergyTokenClient};
+use soroban_sdk::{testutils::Address as _, Address, Env};
+
+fn setup() -> (Env, EnergyTokenClient<'static>) {
+    let env = Env::default();
+    env.mock_all_auths();
+    let id = env.register(EnergyToken, ());
+    let client = EnergyTokenClient::new(&env, &id);
+    let admin = Address::generate(&env);
+    let minter = Address::generate(&env);
+    client.initialize(&admin, &minter);
+    (env, client)
+}
+
+// ── mint: balance overflow ────────────────────────────────────────────────────
+
+#[test]
+#[should_panic(expected = "overflow: balance")]
+fn mint_overflows_recipient_balance() {
+    let (env, client) = setup();
+    let user = Address::generate(&env);
+    // Fill balance to i128::MAX
+    client.mint(&user, &i128::MAX);
+    // Any positive mint must now overflow
+    client.mint(&user, &1_i128);
+}
+
+// ── mint: total_minted overflow ───────────────────────────────────────────────
+
+#[test]
+#[should_panic(expected = "overflow: total_minted")]
+fn mint_overflows_total_minted() {
+    let (env, client) = setup();
+    let a = Address::generate(&env);
+    let b = Address::generate(&env);
+    // Two recipients — balance per address is fine, but total_minted overflows
+    client.mint(&a, &i128::MAX);
+    client.mint(&b, &1_i128);
+}
+
+// ── mint: zero and negative amount rejected ───────────────────────────────────
+
+#[test]
+#[should_panic(expected = "amount must be positive")]
+fn mint_zero_amount_rejected() {
+    let (env, client) = setup();
+    let user = Address::generate(&env);
+    client.mint(&user, &0_i128);
+}
+
+#[test]
+#[should_panic(expected = "amount must be positive")]
+fn mint_negative_amount_rejected() {
+    let (env, client) = setup();
+    let user = Address::generate(&env);
+    client.mint(&user, &-1_i128);
+}
+
+// ── burn: underflow (burn more than balance) ──────────────────────────────────
+
+#[test]
+#[should_panic(expected = "insufficient balance")]
+fn burn_underflows_when_amount_exceeds_balance() {
+    let (env, client) = setup();
+    let user = Address::generate(&env);
+    client.mint(&user, &100_i128);
+    client.burn(&user, &101_i128);
+}
+
+#[test]
+#[should_panic(expected = "insufficient balance")]
+fn burn_underflows_on_zero_balance() {
+    let (env, client) = setup();
+    let user = Address::generate(&env);
+    // No mint — balance is 0
+    client.burn(&user, &1_i128);
+}
+
+#[test]
+#[should_panic(expected = "amount must be positive")]
+fn burn_zero_amount_rejected() {
+    let (env, client) = setup();
+    let user = Address::generate(&env);
+    client.mint(&user, &100_i128);
+    client.burn(&user, &0_i128);
+}
+
+// ── transfer: sender underflow ────────────────────────────────────────────────
+
+#[test]
+#[should_panic(expected = "insufficient balance")]
+fn transfer_underflows_sender() {
+    let (env, client) = setup();
+    let from = Address::generate(&env);
+    let to = Address::generate(&env);
+    client.mint(&from, &50_i128);
+    client.transfer(&from, &to, &51_i128);
+}
+
+// ── transfer: recipient balance overflow ──────────────────────────────────────
+
+#[test]
+#[should_panic(expected = "overflow: recipient balance")]
+fn transfer_overflows_recipient_balance() {
+    let (env, client) = setup();
+    let from = Address::generate(&env);
+    let to = Address::generate(&env);
+    // Give `to` a balance near i128::MAX
+    client.mint(&to, &(i128::MAX - 10));
+    // Give `from` enough to trigger overflow on recipient
+    client.mint(&from, &20_i128);
+    client.transfer(&from, &to, &20_i128);
+}
+
+#[test]
+#[should_panic(expected = "amount must be positive")]
+fn transfer_zero_amount_rejected() {
+    let (env, client) = setup();
+    let from = Address::generate(&env);
+    let to = Address::generate(&env);
+    client.mint(&from, &100_i128);
+    client.transfer(&from, &to, &0_i128);
+}
+
+// ── burn_from: underflow ──────────────────────────────────────────────────────
+
+#[test]
+#[should_panic(expected = "insufficient balance")]
+fn burn_from_underflows_when_balance_exhausted() {
+    let (env, client) = setup();
+    let owner = Address::generate(&env);
+    let spender = Address::generate(&env);
+    client.mint(&owner, &10_i128);
+    client.approve(&owner, &spender, &50_i128);
+    client.burn_from(&spender, &owner, &11_i128);
+}
+
+#[test]
+#[should_panic(expected = "insufficient allowance")]
+fn burn_from_underflows_allowance() {
+    let (env, client) = setup();
+    let owner = Address::generate(&env);
+    let spender = Address::generate(&env);
+    client.mint(&owner, &100_i128);
+    client.approve(&owner, &spender, &5_i128);
+    client.burn_from(&spender, &owner, &6_i128);
+}
+
+// ── approve: negative amount rejected ────────────────────────────────────────
+
+#[test]
+#[should_panic(expected = "amount must be non-negative")]
+fn approve_negative_amount_rejected() {
+    let (env, client) = setup();
+    let owner = Address::generate(&env);
+    let spender = Address::generate(&env);
+    client.approve(&owner, &spender, &-1_i128);
+}
+
+// ── transfer_from: recipient overflow ────────────────────────────────────────
+
+#[test]
+#[should_panic(expected = "overflow: recipient balance")]
+fn transfer_from_overflows_recipient() {
+    let (env, client) = setup();
+    let owner = Address::generate(&env);
+    let spender = Address::generate(&env);
+    let to = Address::generate(&env);
+    client.mint(&owner, &20_i128);
+    client.mint(&to, &(i128::MAX - 10));
+    client.approve(&owner, &spender, &20_i128);
+    client.transfer_from(&spender, &owner, &to, &20_i128);
+}