Growth in the U.S. service sector slowed for a second consecutive month in September, suggesting the rise in energy prices is limiting the economic expansion.

The Institute for Supply Management’s measure of financial services, construction, retail and other non-manufacturing enterprises declined to 56.7 for the month, the lowest reading since May 2003, from August’s 58.2. The gauge has still shown expansion, marked by readings higher than 50, since April 2003.

The ISM services index reached a record of 68.4 in April.

Economists had forecast the services index to rise to 59 in September.

A measure of new orders for non-manufacturing companies fell to 58.5 from 58.6. The index of order backlogs fell to 52.5 from 53. The inventory index dropped to 51.5 from 53 in August. The survey’s employment index rose to 54.6, the highest since June, from 52.5.

The index of prices paid, a measure of costs for purchased materials and services, fell to 67.1 last month, the lowest since March, from 70 in August.

The indexes for business activity, orders, prices and employment are adjusted for seasonal variations. All others are unadjusted. Services account for about 85 percent of the $11.6 trillion gross domestic product of the U.S.

Last week the group reported that its index of U.S. manufacturing fell in September to 58.5, its lowest level in a year, as factories reported slower fewer orders. The manufacturing index reached a 20-year high of 63.6 in January.