Same again, JSR at the same time as you buy your pellets. Get JSR own brand of gas. £29.95 per 100. Don't think you will get a better quality gas if you pay more - you won't! I've used 100s of JSR without a problem.
Some will recommend Crosman as they contain oil, but Dynamit Nobel who were the importers of the Umarex/RWS C225 strictly advised against them, because the oil gummed up the inner workings of the guns.
Walther CP-2 Match, FAS 604 & Tau 7 target pistols, Smith & Wesson 6" & 4" co2 pistol, Crosman 1377,
Baikal IZH 53 pistol, Gamo CFX Royal,177, Umarex SA-10 CO2 pistol.