Sovereign wealth funds, the massive investment pools run by foreign governments, are now among the biggest speculators in the trading of oil and other vital goods like corn and cotton in the United States, according to interviews with brokers who handle their investments at leading Wall Street banks, veteran traders and congressional investigators. Some lawmakers say the unregulated activity of sovereign wealth funds and other speculators such as hedge funds has contributed to the dramatic swing in oil prices in recent months. The agency regulating the market said it had not picked up on this activity by sovereign wealth funds. In a June letter, the Commodity Futures Trading Commission told lawmakers that its monitoring showed that these funds were not a significant factor in commodity trading. But the CFTC is not detecting the growing influence of foreign funds because they invest through Wall Street brokers known as swap dealers" who often operate on unregulated markets. For this reason, the extent of their activities may be known only to the swap dealers at investment banks such as Goldman Sachs, Lehman Brothers and Morgan Stanley, which handle such transactions. The foreign funds involved in commodity trading are ... mainly from countries ... in Asia that do not already make money from producing oil. While it is difficult to quantify how large foreign funds have become, they now represent 12 percent or more of the overall commodity business for some of the largest investment banks, said an industry veteran who spoke on condition of anonymity.