2010 Lexus IS 250 Owners Manual - Page 625

6-1. Specifications Fuel information Your vehicle must use only unleaded gasoline. IS250C Premium unleaded gasoline with an octane rating of 91 (Research Octane Number 96) or higher required for optimum engine performance. If 91 octane cannot be obtained, you may use unleaded gasoline with an octane rating as low as 87 (Research Octane Number 91). Use of unleaded gasoline with an octane rating lower than 91 may result in engine knocking. Persistent knocking can lead to engine damage and should be corrected by refueling with higher octane unleaded gasoline. IS350C Premium unleaded gasoline with an octane rating of 91 (Research Octane Number 96) or higher required for optimum engine performance. If 91 octane cannot be obtained, you may use unleaded gasoline with an octane rating as low as 87 (Research Octane Number 91). Use of unleaded gasoline with an octane rating lower than 91 may result in engine knocking and significantly reduced performance. Persistent knocking can lead to engine damage and should be corrected by refueling with higher octane unleaded gasoline. At minimum, the gasoline you use should meet the specifications of ASTM D4814 in the U.S.A. and CGSB3.5-M93 in Canada.