Abstract This paper investigates whether tax evasion opportunities can increase tax revenue. Past theoretical discussions have presented mixed outcomes as to whether allowing taxpayers to opt into uncertainty could indeed enhance overall tax revenues. In this study, we conducted a series of original real-effort experiments in an online setting with almost 6,000 participants to test this hypothesis empirically. Our findings show significant positive labour supply responses to the opportunity to evade (increased labour supply by 30%). More importantly, the expected tax revenue significantly and substantially increased by up to 40%. Strikingly, this effect persists when comparing effective tax rates: Lowering effective tax rates through probabilistic enforcement (the opportunity to evade) is more efficient than simply lowering statutory tax rates. Our findings suggest that the opportunity for tax evasion can increase tax revenues beyond what a corresponding decrease in nominal rates would achieve.