Rate Basis
Most sites pay on some sort of hourly usage or points basis. Some pay a fixed rate per hour and some pay a rate based on their ad revenues. Currently the fixed rate sites usually pay a higher rate. The sites that pay based on ad revenues potentially could end up paying more than the fixed rate sites. To do that they will have to have enough users that they can charge more for their ads. While fixed rate sites might change their rates from time to time the ones most likely to stay in business will have to be conservative with their payout rate. If they fix it so high that their ad revenues don't cover their payouts and expenses they won't stay in business long. Of course the same could happen to a revenue based payout site. If their payout percentage uses up too much of their revenue they might not be able to cover expenses which means they could go broke. The payout rate is shown for sites that list it.

Where a recent actual per hour payout rate is known it is shown in parenthesis.