Jacobs' stock was down $3.04 a share, or 6.5%, at $43.61 in afternoon trading after being down more than 9% earlier in the session.
The drop in global oil prices impacted the Pasadena-based company because it's causing energy companies to think twice about spending for new projects.
"Current headwinds caused by energy and commodity prices" are a key reason why "we continue to be cautious in our short-term outlook," Jacobs Executive Chairman Noel Watson said in a statement.
Jacobs said earnings for its fiscal second quarter ended March 27, adjusted for restructuring costs and other special items, fell 16.2% from a year earlier to $91.6 million, or 72 cents a share. Analysts had expected 79 cents a share, according to Factset Research.
The company also lowered its adjusted earnings forecast for its full fiscal year to $2.90 to $3.20 a share from the $3.34 analysts had forecast.
Jacobs said its fiscal second-quarter revenue slipped 2.3% to $2.90 billion, and its order backlog was $18.9 billion as of March 27, up 2.5% from a year earlier.