The induction time of ignition of 1% CH4 [74-82-8] in air was markedly shortened by the addn. of 0.1% C2H6 [74-84-0], C3H8 [74-98-6], or iso-C4H10 [75-28-5]. A computer modeling study of the induction times was done with the use of a recent flame chem. model; the ignition delay times of CH4 alone and their acceleration by the hydrocarbon additives can be quant. accounted for if 10% decay of CH4 is used as the induction time criterion.