The Santa Barbara County Sheriff's Office Coroners Bureau says 53-year-old Gary Bishop and 49-year-old Christopher Avila died of carbon monoxide poisoning.
The men were first reported missing on June 30th after no one heard from them for a day.
Deputies say they were transporting Bishop's boat from the Channel Island Harbor in Ventura to Port San Luis.
The U.S. Coast Guard found the missing vessel later that night.
The boat was discovered 20 miles southwest of the Santa Barbara Harbor.
Investigators say the carbon monoxide poisoning was accidental.