An oil rig off the Dorset coast set up to explore reserves will continue for a month longer than originally planned.
Drilling in Poole Bay was initially set to last three weeks when it began at the start of February.
Corallian Energy is drilling more than 1,000m (3,280ft) below the seabed to investigate oil reserves.
Two council leaders said the drilling had been granted an extension by government regular OPRED. It will now continue until the end of March.
Councillor John Beesley, leader of Bournemouth council, said: "We understood... that to comply with the approved mitigation measures, the applicant's operations must be completed by the end of February, so we are surprised to learn that an extension has been approved.
"Bournemouth council was not consulted or invited to comment... which is deeply disappointing."
Poole Council leader Janet Walton added: "Borough of Poole is extremely disappointed to learn that the [exploration well] has been granted an extension.
"We will be monitoring the situation closely to seek every reassurance that Corallian Energy is compliant with the Environmental Impact Assessment mitigation measures set in place."
Corallian confirmed the extension had been granted.
The BBC understands it was requested after poor weather delayed the start of drilling. It is also likely operations may be concluded before 31 March.
OPRED has been approached for comment.
Protesters have argued that the coast and marine life could be damaged.
However, Corallian said the well would be plugged and the platform removed once work was complete, and the operation would not result in any significant effects to the marine ecosystem.
The 98/11-E well, 6km (3.7 miles) south of Studland, aims to investigate reserves found by British Gas and BP in 1986, called the Colter prospect.
If oil can be economically produced, Corallian proposes extracting it by drilling horizontally from the shore. However, such a scheme would require a separate licence.