itll take a few years for a gallon of fuel to turn into an oily substance and it depends wer its kept and wat temps are....if its in a sealed dark container in a dark and cool dry place wer sun and moisture cant hit it it can be stored for ageeeesss but u should not be using fuel more than 3 months old (recommended) but if ur crazy like dracy u can use 1 year old fuel like her did