Albert Barnes on Matthew 26:16

Sought opportunity to betray him. Luke adds, "in the absence of the multitude." This was the chief difficulty, to deliver him into the hands of the priests so as not to have it known by the people, or so as not to excite tumult. The opportunity which he sought, therefore, was one in which the multitude would not see him, or could not rescue the Saviour.

To betray him. The word means to deliver into the hands of an enemy by treachery or breach of trust; to do it while friendship or faithfulness is professed. All this took place in the case of Judas. But the word in the original does not necessarily imply this. It means simply to deliver up, or to give into their hands. He sought opportunity how he might deliver him up to them, agreeably to the contract.