* Transatlantic arb window seen closing
* LR market rates seen capped
LONDON, Oct 3 (Reuters) - Clean tanker rates for refined petroleum products on top export routes were mostly weaker on Wednesday with the transatlantic market hit by growing availability of vessels.
Rates for medium-range (MR) tankers for 37,000 tonne cargoes from Rotterdam to New York were at W130.42, or $7,526 a day when translated into average earnings, compared with W131.46 or $7,752 a day on Tuesday and W142.71 or $10,137 a day last Wednesday.
Rates were at their highest in six months in late September before momentum faltered as more vessels competed for business.
"There are a decent amount of cargoes to be moved transatlantic, however tonnage is in sufficient supply to keep rates in check for the time being," broker Fearnleys said.
In April last year, rates reached their highest since 2008 on a jump in U.S. gasoline demand, helping reduce the number of tankers available for hire. Since then, average earnings have remained volatile.
"Strong demand for gasoline in the U.S. has lifted margins for European refiners," said Arctic Securities analyst Erik Nikolai Stavseth.
"The transatlantic flow of gasoline has provided some support to the product tanker market. However, with the driving season coming to an end, there is downside to these volumes and likely also resulting in softer freight rates near-term."
Average earnings per day are calculated after a vessel covers its voyage costs such as bunker fuel and port fees. Negative rates indicate costs are greater than earnings.
Analysts said reduced refinery capacity in the Atlantic Basin could boost long-haul demand for the wider products tanker sector in coming years, helped by the delivery of fewer tankers.
Typical Long Range 2 or LR2, 75,000 tonne shipments on the Middle East Gulf to Japan route were at W100.50 on Wednesday in the worldscale measure of freight rates, or $9,478 a day when translated into average earnings, from W100.23 on Tuesday or $9,309 a day and W98.41 or $8,587 a day last Wednesday. In July rates hit their highest level since late October of 2011.
Long Range 1 tankers, carrying 55,000 tonne loads from the Middle East Gulf to Japan, were at W109.77 on Wednesday, from W110.42 on Tuesday and W111.42 last Wednesday.
Brokers said a surplus of vessels was capping upside rate movements in both LR markets.
"LR1 owners ... struggled to maintain last week's fixing level and some fixtures have been concluded at a W107.5 basis," Fearnleys said.
In the Mediterranean, 30,000 tonne shipments ex-Algeria to southern Europe were at W157.78 on Wednesday, versus W158.14 on Tuesday and W160.34 last Wednesday.
(Reporting by Jonathan Saul; Editing by Anthony Barker)
Keywords: TANKERS SHIPPING/PRODUCTS