As the popularity of online bill payments grows, a new study by Mass.-based TowerGroup finds that banks may have to pay upwards of $1 billion by 2010 in online bill pay-related costs and services.

TowerGroup estimates that nearly 24 million consumers are currently active users of online banking bill payment in the U.S., and that the volume of online bill payments will reach 3.87 billion transactions by 2012.

According to the study, the traditional benefits of offering online bill pay, including increased customer retention and enhanced convenience, are no longer compensating for the hard costs associated with administering the service.

One potential way to offset these costs could include charging users a premium to have their online bill payments “expedited,” or posted within 24 hours, according to the study. TowerGroup predicts that by 2010, payments posted within 24 hours of coming due could generate $40.7 million in fee revenue for financial services institutions, offsetting approximately 4 percent of that year’s online bill pay costs.