# Gas mileage (87 octane vs 89 octane) **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [April 19, 2008, 3:25pm UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055 "2008-04-19T15:25:50Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![castaway081](https://avatars.discourse-cdn.com/v4/letter/c/9f8e36/32.png) [@castaway081](https://community.cartalk.com/u/castaway081)\ **Post date:** [April 19, 2008, 3:25pm UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055/1 "2008-04-19T15:25:50Z")
Does anyone know how much better gas mileage you may get when driving by using gasoline with higher octane. In this case 87 octane vs 89 octane. ---
**Author:** ![BustedKnuckles](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bustedknuckles/32/25_2.png) [@BustedKnuckles](https://community.cartalk.com/u/BustedKnuckles)\ **Post date:** [April 19, 2008, 3:39pm UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055/2 "2008-04-19T15:39:13Z")
If your car was designed for 87 octane, ABSOLUTELY NONE! If your car was designed for 89 octane, a slight improvement as the engine will run better. 87 octane will cause a decrease in mileage as the engine management system will ‘tune-down’ the engine to cope with the lesser octane fuel. ---
**Author:** ![lenjack](https://avatars.discourse-cdn.com/v4/letter/l/f475e1/32.png) [@lenjack](https://community.cartalk.com/u/lenjack)\ **Post date:** [April 20, 2008, 1:52am UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055/3 "2008-04-20T01:52:32Z")
It is entirely possible that using higher octane than needed will LOWER your mileage! ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [April 20, 2008, 9:43am UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055/4 "2008-04-20T09:43:27Z")
Don’t confuse octane with the quality, or power of fuel Octane is just a rating of how fast the fuel burns. If you have a high performance car with an engine designed for high octane then it needs high octane gas to provide maximum power and in some situations it needs it to provide max mileage, but that is not common. High octane gas is just a little slower burning. You don’t need to know all that. All you need do is to find out what fuel the manufacturer specifies or recommends. If it is specified then you must use it or risk engine damage. If it is recommended, then not using it will result in less power and maybe less mileage. ---
**Author:** ![SteveF](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/stevef/32/2_2.png) [@SteveF](https://community.cartalk.com/u/SteveF)\ **Post date:** [April 20, 2008, 1:36pm UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055/5 "2008-04-20T13:36:19Z")
Most likely you will see no difference. 89 Octane gas is not better, nor more power-packed, than 87 octane gasoline. The only significant difference is the rate of burn. Your computer-controlled engine can make slight adjustments in either case. Any difference in the resulting mpg would be too small for a car owner to measure. ---
**Author:** ![andrew\_j](https://avatars.discourse-cdn.com/v4/letter/a/91b2a8/32.png) [@andrew\_j](https://community.cartalk.com/u/andrew_j)\ **Post date:** [April 21, 2008, 12:39am UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055/6 "2008-04-21T00:39:53Z")
Try it and see. Very easy to try. If your car only needs 87 I would stick to it. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [April 21, 2008, 7:42pm UTC](https://community.cartalk.com/t/gas-mileage-87-octane-vs-89-octane/13055/7 "2008-04-21T19:42:02Z")
None. High performance engines don’t use higher octane for better performance, they use it because their higher compression requires it to prevent preignition. The heat generated by high compression can cause low octane fuel to ignite before it’s supposed to.