LONDON, Dec 9 (Reuters) - Clean tanker rates on major export routes were mainly steady on Monday, with expectations of further support in the transatlantic market due to tighter vessel availability.

Rates for medium-range (MR) tankers for 37,000 tonne cargoes on the TC2 route from Rotterdam to New York were at W115.00 in the Worldscale measure, or $7,281 a day when translated into average earnings.

That compared with W112.50 or $6,691 a day on Friday and W113.33 or $6,974 last Monday. In recent months, average earnings have slid to their lowest levels since they were first compiled in 2008, exchange data showed.

“The general MR trade on the Continent ... has been steady, and MRs are tight,” broker E.A. Gibson said.

Broker SSY said separately there had been bookings to South America, the United States and West Africa.

“There could be scope for rates to firm if charterers struggle to cover particular cargoes,” SSY said.

Average earnings per day are calculated after a vessel covers its voyage costs such as bunker fuel and port fees.

In contrast, rates for MR tankers on the U.S. Gulf (USG) to Europe route were weaker at W107.50 or $6,464 a day. That compared with W109.64 or $6,976 on Friday and W121.43 or $9,965 a day last Monday.

“On the other side of the Atlantic, rates in the USG are softening amid ample tonnage and reduced enquiry. Ships are failing at current levels, so further softening may be expected,” SSY said.

Last month, rates on that route rose to their highest level since earnings were published in June 2012, Baltic Exchange data showed. Buoyant demand for diesel products has boosted tanker activity on the U.S. Gulf to Europe route, known as the backhaul journey as vessels usually travel to the U.S. east coast first and then pick up return cargoes.

Long Range 1 tankers, carrying 55,000 tonne loads from the Middle East Gulf (MEG) to Japan, reached W100.91 or $7,486 a day and were at their highest level since late October. That compared with W97.45 or $6,296 a day on Friday and W89.41 or $3,359 a day last Monday.

Larger Long Range 2 or LR2, 75,000 tonne shipments on the Middle East Gulf to Japan route were at W82.15 or $7,974 a day. That compared with W82.35 or $8,136 a day on Friday and W77.00 or $5,592 last Monday.

“The MEG LR2 market has firmed steadily over the course of the (past) week. Tonnage looks increasingly tight for end-December dates and activity for the period is strong,” SSY said.

“LR1 rates jumped at the end of the week for similar reasons. Owners are increasingly bullish and will be looking for further gains.”