WILMINGTON, Del. — By state, the drivers who owe Delaware the most in unpaid tolls and penalties are from Maine, according to state records.

Sound surprising? That’s because only their license plates come from Maine.

Thousands of Delawareans are illegally registering boat, horse, farm and other trailers with Maine, where it’s cheaper and no safety inspection is required.

It’s also illegal under Delaware law.

“We want to ensure the trailers are inspected and fit to operate on Delaware roads without safety concerns, such as detachment or collapse,” said state police Sgt. Paul Shavack.

Unlike most states, Maine allows nonresidents to register trailers for one to 12 years at a time, at a fraction of what other states charge — about $12 versus at least $40 in Delaware. Agents also make it easy to register via mail, fax or email.

That accounts for the disproportionate number of trailers with Maine tags, towed by vehicles with Delaware tags. State officials don’t know the exact number of such trailers, but they say it’s growing.

The problem at toll plazas is that the trailers shield the license plates of the towing vehicles, so it’s more difficult to track down toll cheats.

“These ‘Maine’ trailers are a big chunk of our out-of-state toll violators,” said Jennifer Cohan, director of the state Division of Motor Vehicles.

Last fiscal year, the division traced a quarter of the $1.26 million owed in delinquent tolls on Interstate 95 and Del. 1 to violators with Maine tags.

Neither Delaware nor neighboring states and tolling authorities can enforce unpaid tolls across state lines. Officials hope to change that soon with legislation allowing for state-to-state reciprocity.

State Transportation Secretary Shailen Bhatt said such a bill is among his legislative priorities in this session and could help the state recoup an estimated $1.5 million a year. As chair of an interstate alliance of transportation and toll agencies, Bhatt is urging members of the I-95 Corridor Coalition to do the same.

Last year, three states — Massachusetts, New Hampshire and, yes, Maine — entered the first-ever reciprocity agreement to pursue the vehicle registrations of out-of-state toll violators.

“All the participating states have seen an increase in payment of tolls, which is why we want to emulate what they’re doing,” Cohan said.

“It takes legislation in the surrounding states, as well. We’ll be looking to secure agreements with Maine, Maryland, New Jersey, and all the regional states will be doing the same.”

In the meantime, the Division of Motor Vehicles and state police are contacting the trailer-toting community to explain their concerns.

They also will remind drivers that residents have 60 days after moving here to register vehicles and trailers in Delaware. The only exception is for vehicles covered under the International Registration Plan — usually, 18-wheeled tractor-trailers.

In 2010, lawmakers increased the penalty for failing to register a vehicle within 60 days from a $25 fine to a minimum $400.

Maine’s program for trailer registrations is a revenue loss for Delaware and other states, with several complaining to the American Association of Motor Vehicle Administrators, said Catherine Curtis, the association’s director of vehicle programs.

Trailer registrations account for $13.7 million of the annual revenue generated by vehicle registrations in Maine, said Barbara Redmond, Maine’s chief deputy secretary of state.

She said Maine has nearly 771,000 registered long-term trailers and 280,000 annual trailer registrations. Officials would not provide a breakdown of registrations by residency.

Delaware has roughly 35,600 registered trailers, not including semi- or tractor-trailers.