The United States led the world in both purchases and sales of credits in the $387 million voluntary carbon market last year, as the market at once contracted and became more interconnected, according to the fourth annual State of the Voluntary Carbon Markets Report released today.

The average price of carbon credits in the over-the-counter market slipped about 12 percent from $7.30 per tonne to $6.50 per tonne, said the report issued by Ecosystem Marketplace and Bloomberg New Energy Finance. Volumes dropped about a quarter in response to the global financial crisis as companies cut spending in corporate social responsibility and as government climate plans stalled in the United States and Australia.

Although the economic downturn reduced offset purchasing for corporate social responsibility, the report notes significant growth in the pre-compliance segment of the voluntary markets. These are speculative credits bought in anticipation of a cap-and-trade program in the United States, which accounted for the greatest market share of supply (56 percent) and demand (49 percent) of voluntary carbon credits in 2009.

“The economic recession had a marked impact,” Milo Sjardin, Bloomberg New Energy Finance Director and report co-author, said in a statement.

The most popular project types generating emission reductions (41 percent of all transactions) were those that destroy methane – a greenhouse gas that traps more than 20 times as much heat as carbon dioxide.  Forestry projects were next (24 percent), followed by renewable energy projects (17 percent).

The US took the lead from Asia as the source of the vast majority of offset credits (56 percent), followed by Latin America (16 percent) and Asia (12 percent).

“Expectations of a possible US carbon trading program lifted the importance of the US, which figured as the largest buyer and seller in the market and the most popular transactions were those that could count towards future compliance,” Sjardin said. “However, with the current state of play of US politics this situation is likely to be very different this year.”