Disclosed is an effective thermal grease comprising a hyperbranched olefinic fluid and a thermally conductive filler. Property-modifying additives and fillers may also be included. The hyperbranched olefinic fluid is selected to have an average of at least 1.5 methine carbons per oligomer molecule and at least 40 methine carbons per one thousand total carbons. The thermal grease exhibits a flash point of 180° C. or higher, a pour point of 0° C. or lower, and a kinematic viscosity at 40° C. of no more than 200 cSt (0.0002 m 2/s). The composition may offer improved thermal conductivity, reduced tendency to migrate, and lower cost when compared with many other thermal greases, including silicone-based thermal greases.