Four companies were given the OK to bypass the federal bar of using drones for commercial purposes—for construction site monitoring and oil rig flare stack inspections, regulators said Wednesday.

"Unmanned aircraft offer a tremendous opportunity to spur innovation and economic activity by enabling many businesses to develop better products and services for their customers and the American public," said Transportation Secretary Anthony Foxx. “We want to foster commercial uses of this exciting technology while taking a responsible approach to the safety of America’s airspace."

The Federal Aviation Administration has maintained since at least 2007 that the commercial operation of drones is illegal. Earlier this year, it began slowly granting exceptions on an application-by-application basis.

A federal judge ruled in March that the FAA enacted the regulations illegally because it did not take public input before adopting the rules, which is a violation of federal law. Flight regulators appealed the decision, which was reversed last month.

The companies winning exemptions Wednesday were Trimble Navigation Limited, (PDF) VDOS Global, (PDF) Clayco Inc. (PDF) and two (PDF) exemptions (PDF) for Woolpert Inc. In September, the FAA granted Hollywood the right to use drones when making films.

Foxx said all the exemptions to the bar of commercial drone use were allowed because the operations do not pose a risk to the national airspace or national security. The drones are required to be within eyesight of the operators, the FAA said.

"The FAA’s first priority is the safety of our nation’s aviation system," FAA Administrator Michael Huerta said. "Today’s exemptions are a step toward integrating UAS [unmanned aircraft system] operations safely."

In all, the agency said it has received 167 requests for exemptions to the law barring the commercial use of drones. The FAA had promised that it would revisit the commercial application of small drones with potential new rules in place perhaps by the end of 2015. The agency said Wednesday, however, that it might be 2017 until it finalizes regulations.

Amazon.com has proposed delivering packages by drones.