Racing Victoria will pay a rebate to approved wagering agencies in a six-month trial aimed at stopping big punters from betting with unlicensed offshore operators.

RV's research identified the need to keep punters that win less than four per cent on turnover nearing $500,000 from shifting their business to unlicensed or illegal companies.

The punters in the `High Volume, Low Margin' category account for less than eight per cent of domestic betting on Victorian racing but are those most likely to take advantage of a lack of federal legislation to prevent them betting with unlicensed agencies, the research found.

Victoria's 300 approved wagering service providers can apply to claim a rebate of up to one per cent, which will be subject to an audit and transparency protections from RV during the trial period to help them provide a better service to the targeted punters.

"The expectation from the trial is that it will enable (providers) to grow this segment of the market and prevent customers betting offshore with unlicensed operators," Racing Victoria's Andrew Catterall said in a statement.

RV has no concrete figures on the amount of illegal overseas betting on Victorian racing but the governing body views the market as a threat to the sport's integrity and revenue sources.

"Unlicensed offshore operators do not pay race fields (fees) and hence make no economic contribution to the sustainability of the Victorian racing industry," Catterall said.

"More importantly, such wagering operators do not have information sharing agreements with RV and therefore betting activity being conducted with them is unable to be monitored."

Catterall said he expected the initiative to produce an increase in net revenue to the Victorian industry.

Total turnover on Victorian racing in July increased by more than five per cent on last year's figures.