Online payment security remains a concern for consumers, and according to a new study, that concern could mean online retailers in the U.S. are leaving a lot of cash on the table.

According to a recent survey by Javelin Strategy & Research commissioned by direct carrier biller PaymentOne, 4 out of 5 consumers would spend more money online if they had an easier, more secure payment method. And that could add up to some real money. Javelin found that online retail could add $109.8 billion by adding an alternative payment method at checkout that doesn't require a credit card.

"If digital merchants simply offered consumers an alternative way to pay, such as mobile carrier based payments, 79 percent of decisive consumers indicated they would spend more, driving significant new incremental revenue from subscriptions, transactions and purchases," said Phil Blank, managing director at Javelin Strategy & Research.

Blank said that the estimated $110 billion in new revenue for online merchants in the U.S. represents a massive untapped opportunity.

Mobile payments vs plastic

The study found that many consumers had concerns that using credit cards online, especially for small digital purchases, put their privacy and security at risk. Fifty-five percent of respondents said they worried a merchant or website will start sending them junk email after a purchase, and 54 percent worried their personal information will be sold to other merchants. Over half (51 percent) said they are concerned that credit card information will be intercepted.

Interestingly, the survey found that alternatives to credit cards, including some mobile payment methods, are actually viewed by consumers as more secure than credit cards. According to the report, respondents felt online purchases billed directly to a mobile phone bill are more secure than credit cards by a margin of nearly 4 to 1. Of alternative payment methods to credit and debit cards, 58 percent of those surveyed said they prefer direct carrier billing.

"Consumers' concerns around the security and privacy of online payment transactions are staring digital merchants in the face and demanding attention," said PaymentOne EVP Brad Singer in a statement.

"In today's economy where every cent counts and every customer is vital to the success of a business, merchants clearly need to do more to ensure customers aren't scared away when it comes time to check out," Singer said. "The implementation of new consumer-friendly alternative payment options may well be the single most important step merchants and publishers can take to grow their customer bases and their revenues."

The Javelin study, entitled "2011 Online Payment Poll," was conducted in September 2011 and surveyed over 2,000 U.S. consumers.