(from Shell's Web Site on the topic of Research Octane Number (RON) versus Motor Octane Number (MON)) The difference between the two measurements is caused by the engine’s operating conditions, and the Research ® octane number is usually nine to eleven numbers higher than the Motor (M) octane number. Our manuals state that we need a RON of at least 95 - Is it safe to say that with that 9 to 11 point spread, that the (R+M)/2 number that's marked on the pump is within half of that spread - 4.5 and 5.5 below that gasoline's RON, or is it remotely possible that a gasoline might have a smaller difference between its R and M? If Shell's 9-to-11 point guideline is solid, then a pump marked 91 should have an R of 95.5 to 96.5, no? Has any TT'er heard something different? I can just see myself thinking I'm so smart buying something marked 92, and it actually being some unexpected case of zero R-N difference like (92R+92M)/2 = 92 on the pump and 92 RON!