"made extensive efforts" is a correct and usable phrase in written English.
You can use this phrase to describe an instance in which somebody has taken a great deal of effort to complete a task. For example, "John made extensive efforts to ensure the success of the project."
Mr. Fager said CBS had made extensive efforts to determine what Mr. Davies told the F.B.I.
"We've made extensive efforts to try to find him," said Joshua White, the deputy city attorney trying the case.
But even on that subject, Professor Moglen said, Judge Jackson made extensive efforts to portray his approach as consistent with the law.
He said his team had made extensive efforts to contact the witnesses on Mr. Milosevic's list and had managed to persuade very few to attend.
Merkel and Hollande have made extensive efforts to resolve Ukraine's 16-month pro-Russia uprising and return peace to the EU's turbulent eastern front.
He said his team had made extensive efforts to contact the witnesses on Mr. Milosevic's list but managed to persuade very few to attend.
We made extensive effort to identify good artifact-free emergence epochs, and used 10-30-second 10-30-second 10-30-secondEEG data for the Emergence analysamples
For the reasons listed above, we made extensive effort to identify good artifact-free preoperative epochs, and used 11-second samples of artifact-free EEG data for the awake-state analysis.
We make extensive efforts to adjust analyses for the risk of the patients.
The Royal Thai Government has been making extensive efforts at home and in cooperation with other countries to address the narcotics problem faced by Thailand.
He said the company would build a fence and plant trees and was making extensive efforts to protect the environment around the well sites.
