Discharges in liquid obey time effect, pressure effect and scale effect. Traditional formulas are usually applied in a narrow range to keep the formula form consistent with Martin’s formula. In this paper, we have developed a new empirical formula for the electric strength of transformer oil depending on pulse duration, hydrostatic pressure and gap geometry in form Ebr = κe at-beff Ρ/,sub>spl gamma/ A>sub>-Β d-ϵ to be applied in a wider range. In this formula, the time dependent pressure effect is represented by constant γ, which can be expressed as γ=ape -bpt-c>peff . Time effect, area effect and distance effect are represented by e at-beff, Β and ϵ, respectively. For transformer oil, κ=0.42, a=0.53, b=0.23, ap=0.14, bp=0.93, cp=0.41, Β=0.1 and ξ=0.25±0.06, with Ebr, teff, P, A and d in MV/cm, μs, MPa, cm2 and cm, respectively.