DUI (driving under the influence), DWI (driving while intoxicated), and OWI (operating while intoxicated) are similar criminal offenses that involve the operation of a motor vehicle, electric vehicle, or sometimes an otherwise-powered vehicle—including boats, aircraft, and bicycles—by an operator who is under the influence of or intoxicated by alcohol or drugs. Per se (pronounced purr-say) intoxication is intoxication by definition—as defined in the state’s statutes by blood alcohol concentration (BAC) of .08 or more (.05 in Utah). And even if a person is not per se intoxicated, they may be intoxicated by not having the normal use of their mental or physical faculties (abilities), for example, and may be charged with a criminal offense.

In some contexts the terms DUI and DWI are used interchangeably, with some states using one term and other states using the other term to define what is essentially the same criminal offense. But in some states both criminal charges are available and there is a legal distinction between them.

For example, in some states with both criminal offenses, DUI is the criminal offense of operating a vehicle under the influence of prescription or recreational drugs, and DWI is the offense of operating a vehicle while intoxicated by alcohol. In some states DWI refers to per se intoxication when the driver’s BAC is above the threshold defined by statute—.08 (.05 in Utah)—and DUI is a criminal offense charged when the police officer believes the driver is under the influence of alcohol, despite the driver’s BAC being below the statutory threshold of .08. And in some states DUI is a separate offense for drivers under the legal age of drinking (21) who have some alcohol in their system, but less than a .08 BAC.

These and other similar alcohol-related operating offenses—including aggravated or enhanced forms of these offenses—vary from state to state in their definitions and potential punishments and are generally located in a state’s statutes—often in the penal code or criminal code.

In Maine, the terms OUI (Operating Under the Influence) and DUI (Driving Under the Influence) are used to describe the offense of operating a motor vehicle while impaired by alcohol or drugs. Maine law sets the blood alcohol concentration (BAC) limit at .08 for drivers 21 and over, which is the per se intoxication level. For drivers under the age of 21, Maine has a zero-tolerance policy, meaning any detectable amount of alcohol in their system can result in an OUI charge. The state does not differentiate between DUI and DWI as separate offenses; instead, it uses the term OUI to encompass all forms of impaired driving, whether due to alcohol, illegal drugs, prescription medications, or other substances. Penalties for OUI in Maine can include fines, license suspension, and even jail time, depending on the circumstances such as prior offenses or the presence of aggravating factors.