Microfinance has been found to be less effective for high risk/return borrowing groups. We report a group liability microfinance lab experiment that tests a mechanism to raise repayment rates among such borrowers. The mechanism offers partial revenue sharing among groups of borrowers, agreed to before individual business outcomes are realized and loan repayment is due. Such revenue sharing makes loan repayment optimal under more outcome states, increasing the expected benefit to each borrower of repayment to qualify for future loans. We further test the effect of allowing borrowers to renege on revenue sharing agreements after learning their business outcomes, prior to loan repayment decisions. Our results illustrate the problem that exogenously higher risk/return borrowing groups achieve lower loan repayment rates than lower risk/return borrowing groups. We find evidence that optional revenue sharing significantly increases high risk borrowers’ repayment rates, but that most of this gain is lost if they can renege on revenue sharing agreements.