San Marcos Gas Prices: Regular Spans 48 Cents; Diesel Is $6.899

Regular gasoline prices differ by 48 cents per gallon in the latest verified San Marcos station snapshot, while diesel is listed at $6.899 per gallon at a 7-Eleven on East Mission Road.

Costco San Marcos lists regular gasoline at $5.299 per gallon at 725 Center Drive. A 7-Eleven at 578 E. Mission Road lists regular at $5.779 and diesel at $6.899. The 7-Eleven page says its fuel prices were updated within 24 hours, while the Costco listing says its prices were updated recently and are community-reported.

Regular gas varies by station

The difference between the two listed regular prices is $0.480 per gallon. On a 15-gallon fill-up, choosing the lower listed price would save about $7.20 before considering driving distance, membership requirements or other station-specific conditions.

These are station prices, not an official San Marcos citywide average, and they do not establish that every local station falls within the same range. Costco’s listing also warns that prices may vary and that the pump price at the time of purchase controls.

Diesel remains near $6.90

The cited East Mission Road 7-Eleven lists diesel at $6.899 per gallon. That price matters most for contractors, delivery operators, landscapers, service companies and other businesses whose vehicles use diesel regularly.

Compared with the previous local fuel-price check, the documented regular-gas spread is 2 cents wider, while diesel at the cited 7-Eleven remains at $6.899. The available continuity information does not provide the earlier station-by-station regular prices, so it does not support a precise comparison for either location.

AAA regional context

AAA’s San Diego metro table, in a price check dated August 3, 2026, shows an average of $5.753 for regular gasoline and $6.958 for diesel. The Costco regular price is below that regional average, while the East Mission Road 7-Eleven regular price is slightly above it. The listed 7-Eleven diesel price is slightly below the San Diego metro diesel average.

AAA’s same table shows San Diego metro regular gas at $5.720 a week earlier, $5.435 a month earlier and $4.553 a year earlier. Diesel was $6.873 a week earlier, $6.482 a month earlier and $5.012 a year earlier. Those comparisons indicate that both fuels remain above the listed week-, month- and year-ago regional levels, even though individual San Marcos stations differ substantially.

What drivers and businesses should watch

For households, the local spread makes station shopping meaningful when a fill-up is large or fuel use is frequent. For restaurants, contractors, delivery drivers and service businesses, diesel and gasoline costs can affect route planning, delivery expenses and operating budgets.

Prices can change quickly as station listings are updated. Drivers should check the posted pump price and any membership or payment restrictions before completing a purchase.

What are you seeing around San Marcos? Share the highest and lowest regular-gas or diesel prices you have found locally.

Sources

• 7-Eleven fuel-price page — 578 E. Mission Road
• Costco San Marcos fuel-price listing
• AAA San Diego metro fuel-price table