North American stock markets looked set to extend losses Tuesday, mirroring overseas declines, ahead of the start of second-quarter earnings season.

On Monday, the Toronto Stock Exchange’s benchmark index fell almost 300 points as commodity prices retreated.

On Tuesday, oil prices swung below US$140 a barrel after a plunge of nearly US$4 in the previous session. Light sweet crude was at US$139.11 a barrel, down US$2.26 on the New York Mercantile Exchange session.

Gold declined $4.90 to US$923.90 per ounce on the Nymex, and copper was also lower.

There are no major economic releases from Statistics Canada today.

The Canadian dollar opened at 97.96 cents US. off 0.19 cent.

In business news, WestJet today announced it has signed a memorandum of understanding to build a distribution and codeshare agreement with U.S. based Southwest Airlines. This memorandum of understanding is the first step that will see both airlines, by late 2009, have the ability to commence codeshare flights across both networks.

In earnings news, Jean Coutu Group Inc. lost $20.2 million in its first quarter ended May 31, compared with a year-ago loss of $6.4 million. The latest quarter included $53.4 million as Coutu’s share of the loss of U.S. drugstore chain Rite Aid Corp.

After North American markets close, aluminum producer Alcoa delivers what are expected to be weak earnings to kick off the U.S. second-quarter earnings season.

Overseas, Japan’s Nikkei stock average finished down 2.5% and Hong Kong’s Hang Seng lost 3.2%.

The FTSE 100 fell more than 2% during the morning and was down 1.3% early in the afternoon in London and the French CAC-40 fell 1.8%.

Germany’s DAX index was down 1.7% after global industrial group Siemens AG announced plans to eliminate 4.2% of its workforce – 16,750 positions, mostly administrative.

Falling resources shares pulled the Toronto Stocks Exchange’s benchmark index sharply lower Monday.

The S&P/TSX composite index plunged 297.59 points, or 2.12%, to close at 13,712.80.

The index is now down 120 points from where it started the year.

The junior S&P/TSX Venture composites index plunged 3.3%, or 84.62 points, to end at 2,478.37.

In New York, the Dow Jones industrial average shed 56.58 points, or 0.50% to end at 11,231.96.

The S&P 500 dropped 10.59 points, or 0.84%, to close at 1,252.31. The tech heavy Nasdaq composite index slipped 2.06 points, or 0.09%, to end at 2,243.32.