Eduardo Lopez is accused of nine felonies, including one negligent homicide and eight additional counts of criminal endangerment.
He posted a $100,000 bond on Monday and appeared in front of Judge Landee Holloway.
He could spend up to 100 years in prison and pay hundreds of thousands of dollars in fines if convicted on all counts.
“He was driving down Interstate 90 for approximately 11 miles, driving eastbound in the westbound lane," said Missoula County prosecutor Brittany Williams. "He nearly hit at least, we have information of 12 victims at this time, nearly hit 12 victims head-on.”
Prosecutors say tests results about Lopez’s possible substance use at the time of the wreck are not back yet. They have asked that Lopez, who is originally from Oregon, remain in Missoula County and undergo pretrial monitoring.