Abstract: Synthetic base oils for functional fluids and greases are provided comprising a mixture of monoalkylated naphthalenes and polyalkylated naphthalenes, said naphthalenes represented by the formula: ##STR1## wherein the R' groups are independently selected from H and methyl, the monoalkylated naphthalenes have three R groups which are H and one R group which is a 12-26 carbon alkyl, the polyalkylated naphthalenes have from two to four R groups which are 12-26 carbon alkyl and any remainder R groups H, and the weight ratio of monoalkylated naphthalenes to polyalkylated naphthalenes is from 5:95 to 70:30 when the average alkyl group is C.sub.12 -C.sub.16 and from 5:95 to 99:1 when the average alkyl group is C.sub.17 -C.sub.26. In the preferred mixture, the polyalkylated naphthalenes have a numerical ratio of .alpha./.beta. substitution of from 50/50 to 10/90 when the R' groups are both H.