By car
You will most likely need a car once arriving in Oroville, so it is better to arrive with your own first. Oroville straddles Highway 70 and has four exits off this main thoroughfare.
By train
During Gold Rush times, there were several trains a day down to Sacramento and San Francisco. Today, sadly, there is no direct service whatsoever. The Amtrak Coast Starlight stops in neighboring Chico, but has quite horrible arrival times and frequency to get to Oroville, not mention being a half hour drive from town.
By bus
There are three main bus methods to get to Oroville.
Amtrak (http://www.amtrak.com) - While better known for their trains, Amtrak does run a connecting bus service from their Sacramento hub. In Sacramento you can transfer to trains that will take you nearly anywhere in the country. The number of buses varies a great deal based upon the season and it's best to consult their website to make plans specific to when you want to travel. The stop is not near the center of town though as it is just off the main highway at a gas station, so visitors would need to plan an additional ride accordingly. If the timing works, the hourly B-Line 24 Route (http://www.blinetransit.c...) can connect visitors to the rest of town.
Casino Buses - With the opening of two large Indian gambling casinos in the town several years ago, bus routes were created to link up gamblers in the San Francisco Bay Area with these casinos. The schedules are not ideal, but the cost of the ride is considerably cheaper than any other option given it is offset by the fact that they believe those riding it will be gambling upon arrival. To use this, inquire directly with the Gold Country or Feather Falls Casinos.
Greyhound (http://www.greyhound.com) - The stalwart American bus service. There are at least two regular bus connections with Oroville a day that are exceedingly slow, although they stop closer to the main part of town. The hourly B-Line 25 Route (http://www.blinetransit.c...) is available to connect people to other areas of town.