NEW YORK (Bloomberg) — The cost to transport crude oil from the Caribbean on Aframax tankers fell as port delays eased, freeing ships for new voyages. The availability of ships may drive rates lower next week.

Vessels were hired for an average rate of Worldscale, or WS, 357.5, an 11 percent decrease from May 23, according to Houston-based Lone Star, R.S. Platou and New York-based Poten & Partners. That is equal to about $65,000 per day after expenses such as fuel and port fees.

"The delays are slowly but surely unwinding, and there's been an overabundance of tonnage" in the region, Bruce Kahler, a broker for Lone Star, R.S. Platou, said in an interview today.

Weakness in North Sea and Mediterranean markets are keeping ships in the Caribbean, Kahler said. "The ships are sitting here, saying 'I'll stay here until the market goes down, and then we'll go away again,"' he said.

Rates more than doubled this month, aided by rising margins for US refiners.

The so-called crack spread, the difference between the cost of crude oil and income from selling gasoline and heating oil, has risen 53 percent this month to $18.356 a barrel, based on New York futures prices.

"Demand for crude transport into the US has been buoyed by the upward trajectory of US crack spreads," said Omar Nokta, an analyst at Dahlman Rose & Co. in New York.

ConocoPhillips and Petroleo Brasileiro SA each contracted an Aframax to transit between the Caribbean and the US Gulf Coast, Lone Star said.

Three tankers arrived in the Gulf of Mexico in the past week to call at the Louisiana Offshore Oil Port, or LOOP, the biggest US oil-import terminal, according to data compiled by Bloomberg.

They include: Saudi Arabia's Phoenix Star, a 291,435 deadweight-ton tanker, Arab Maritime Petroleum Transport Co.'s Zallaq, which as a capacity of 153,019 deadweight tons and Marmaras Navigation Ltd.'s Explorer, a 149,325 deadweight-ton ship.

Forty-one crude-oil tankers arrived in the Gulf of Mexico this week, up from 33 last week, according to Bloomberg data.

Bermuda-based Tsakos Energy Navigation Ltd.'s Parthenon is scheduled to arrive in La Salina, Venezuela, today, and Allocean Charters Ltd.'s Sank Brave is due in Puerto de la Cruz, Venezuela, today.

Malaysia's Eagle Anaheim is due in Puerto Jose, Venezuela, on June 1, according to the data.

Worldscale points are a percentage of a nominal rate, or flat rate, for a specific route.

Flat rates, quoted in US dollars a ton, are revised annually by the Worldscale Association in London to reflect changing costs.

The Caribbean is the world's third-largest Aframax-tanker market, after the Mediterranean and Southeast Asia.

An Aframax is the most common tanker used to move oil in the region.