Abstract: A working fluid composition for a compression type refrigerator, comprising:(A) a refrigerant composed of ammonia or at least one hydrofluorocarbon having the number of carbon being not more than 2 and containing no chlorine; and(B) a lubricant for the refrigerator, said lubricant comprising 100 parts by weight of a synthetic oil and 0.5 to 10.0 parts by weight of at least one benzotriazole derivative expressed by the following formula (I). ##STR1## in which R.sup.1 is hydrogen or an alkyl group having the number of carbons being 1-10, and R.sup.2 and R.sup.3 independently indicate an alkyl group having the number of carbons being 4-18.

Abstract: A lubricating oil for flon compressor includes, as a main ingredient, a compound represented by a formula (I):R.sub.1 --[--O--(R.sub.2 O).sub.y --(CH.sub.2 CH.sub.2 O).sub.z --H].sub.x (I)in which R.sub.1 denotes a hydrocarbon residue derived from a C.sub.1-8 alcohol having a valence of 1 to 4, R.sub.2 denotes a C.sub.3-4 branched alkylene group, x denotes an integer of 1-4, and y and z each independently denote a positive number, R.sub.2 O units and CH.sub.2 CH.sub.2 O units are block copolymerized in an order shown in the formula (I), z/(y+z) is more than 0 but not more than 0.3. The lubricating oil has a kinetic viscosity of 2-30 cSt at 100.degree. C. A mixture of the oil having the formula (I) with a lubricating oil having a formula (II): R.sub.3 --[--O--(R.sub.4 O).sub.m --(CH.sub.2 CH.sub.2 O).sub.n --R.sub.5 ].sub.l may be also used. In the formula (II), R.sub.3 denotes a hydrocarbon residue derived from a CI-s alcohol having one to four hydroxyl groups, R.sub.4 denotes a C.sub.