Morgan Stanley posted trading losses on 31 days in the third quarter, the most since 2008 as markets fell amid concern that Europe’s debt crisis may spread.

Traders generated at least $100 million on two days, the fewest in a year, the company said yesterday in a quarterly filing. Three of the daily losses exceeded the firm’s value-at-risk, or VaR, the maximum amount Morgan Stanley estimates it could lose from trading on 95 percent of days.

Morgan Stanley said last month that third-quarter trading revenue dropped 34 percent from the second quarter, excluding accounting gains known as debt-valuation adjustments, or DVA. The company logged three days of losses in the first quarter of 2011 and eight days in the subsequent three-month period.

Morgan Stanley’s derivatives counterparty exposure to MBIA and other bond insurers was $2.1 billion on Sept. 30, up from $1.6 billion on June 30.