Ahead of the Bell: Consumer Price Index

The Labor Department's Consumer Price Index, the government's primary inflation yardstick, is forecast to show a 0.8 percent gain from May, according to the consensus estimate of Wall Street economists surveyed by Thomson/IFR. The data will be released at 8:30 a.m. EDT.

Consumer prices rose 0.6 percent in April, mostly due to volatile food and energy prices.

Gas prices averaged $3.82 a gallon in May, up from $3.51 in April.

The CPI measures the average price change in a basket of goods and services that the typical household is likely to buy monthly, excluding income taxes, stocks, bonds and life insurance. The department collects prices in 87 cities from 50,000 residential units and 23,000 retail and service establishments nationwide. Rent data is collected from about 50,000 landlords or tenants.

The closely watched index helps the Federal Reserve measure the rate of inflation.

Federal Reserve Chairman Ben Bernanke told Congress Tuesday that "numerous difficulties" are racking the economy, and warned that rising prices for energy and food are elevating the risks of inflation.

At the same time, the Labor Department reported that wholesale inflation jumped by 1.8 percent last month, a larger-than-expected gain. Over the past year, wholesale prices have risen 9.2 percent, the most since 1981.