Years ago when you filled up your vehicle with gasoline, the fuel that you bought was 100% gasoline. However, upon the implementation of the Renewable FuelStandardAct of 2007, our gasoline has become blended with ethanol ,so that nowadays when filling up your car with gasoline, it is no longer just gasoline, but in actuality a blend of ethanol and gasoline, to wit the sign at the gas pump will state something to the effect that the gasoline that you are pumping "may contain up to 10% ethanol," which is known in the trade as E10, meaning that the blend is 10% ethanol and 90% gasoline. While there are many arguments, pro and con, as to why we should or shouldn't be using ethanol as a fuel in America, that is a subject for a different day, instead the question being raised is E10 blended gasoline with an octane rating of 87 the same as regular gasoline at the octane rating of 87. The answer is no.
First off, in order to create an octane mixture of 87 with regular gasoline, that mixture actually would contain gasoline at an octane rating of 84, blended with ethanol which has an octane rating of 113. The fact that ethanol has a significantly higher octane rating than gasoline must imply that ethanol is the superior fuel, but in actuality octane does not equate to more power, more fuel efficiency or superiority in any way, but instead refers to the ignition quality of the gas, or in lay terms, the "knocking" of your car engine or the compression ratio necessary for your vehicle's sparkplugs and pistons to generate horsepower. The octane that is necessary for any particular vehicle is listed in your owner's manual and while you can always trade up in octane, there isn't any valid reason to do so, whereas going down in octane from the recommendations of your owner's manual, will increase your risk of engine damage.
In America, most vehicles that are sold run on an octane rating of 87, to which most of that gasoline that is sold for that octane, is a blend of 10% ethanol at an octane rating of 113, with 90% gasoline at an octane rating of 84, making for a combined octane rating of 87. However, the fuel efficiency of an E10 gasoline blend is significantly less than the fuel efficiency of regular gasoline, a fact that most people are not cognizant of. As reported by the midwestenergynews.com, the E10 blend has a lower BTU than regular gasoline, to the tune of 96.67% of gasoline's BTU, which means that E10 will get less gas mileage than regular gasoline and consequently should you be able to find a gas station that is actually selling regular gasoline without any blends to it, you can pay approximately 3.44% higher for that gasoline to achieve the same value for your dollar.
In summary, E10 blended gasoline is not the same as regular gasoline in regards to fuel efficiency, it is inferior by about 3.33% which is the discount that you should receive for utilizing this fuel in your vehicle as compared to regular gasoline. This means that your E10 blended gasoline will consistently get less gas mileage than regular gasoline, because this blended gas is inferior to regular gas for fuel efficiency. America consumed 134,506,764,000 gallons of finished motor gasoline in 2013; one would hope that the environmental "benefits" of ethanol has made up for its inefficiency as a motor fuel.