WASHINGTON — An independent study of oil markets concludes that speculation by large investors was a primary reason for the surge in oil prices during the first half of the year and for the more recent price declines.

It said investors poured $60 billion into oil futures markets during the first six months of the year as oil prices soared from $95 to $145 a barrel and since then have withdrawn $39 billion from those same markets as prices have retreated.

Michael Masters of Masters Capital Management, which did the study, said the flow of money — not major changes in supply and demand — caused the volatile movement of oil prices. The report was released Wednesday by Senate and House sponsors of bills to put additional curbs on oil market speculation.