Repsol said it wrapped up its winter campaign with "encouraging results" from the initial testing of the Quqruk 1 and 6 wells. It encountered an undisclosed level of hydrocarbons in well Quqruk 3.
The company said Alaska is one of the more promising areas in the United States.
"These results are encouraging for the future development of the resources discovered," Repsol said in a statement.
Members of the Alaska House of Representatives said reforming Alaska's tax laws will encourage investors to look at the state's oil reserve potential.
Critics of the measure say it's a handout to oil companies working in the state. Repsol said those tax measures were a critical factor in its work in the North Slope because of the high costs of working in the northern climate, however.
"Exploration can only be carried out during four months of the year, when the terrain is frozen," the company said in a statement.