I buy Sunoco 110 by the 55 gal drum. I typically have some left over from race season to the next. Last year I bought a drum at the beginning of the year and still have half left that'll I'll use this year. I usually put the pump in and pump out what I need and than take the pump out and screw the cap back on. I have been doing this for almost 10 years and haven't noticed any issues doing this. I store the drum in the corner of my heated garage. I'm a bracket racer though and not chasing every last thousandths some guys. My car stays consistent during the course of the day for the weather.