Without the H-1B visa number available at this time, and I could not wait for H-1B visa number application until April of next year, now I am thinking to apply for O-1 visa to work for a dance company. Do I need to have a job offer in advance to apply for O-1 visa? and what are the advantages of O-1 visa over H-1B visa? Thank you.

O-1 visa is an non-immigrant visa for outstanding aliens with extraordinary ability to do specialized work in the United States, in the fields of sciences, arts, athletics, education, and business. As a a basic requirement, a job offer from a U.S. employer is needed to apply for an O-1 visa. Not like H-1B visa, there is no annual number limit for O-1 visa. 

Some important points and advantages of the O-1 visa include:

• the O-1 visa holder can work in the United States legally for the sponsored employer;
• generally, O-1 visa application can be approved fairly quickly;
• the O-1 visas could be approved for the time period necessary for a particular project or event, up to a maximum of 3 years, with unlimited extensions in 1 year increment;
• the O-1 visa holder and his or her family members can travel in or out U.S., as the O visa stamp and status are valid;
• an O-1 visa holder's spouse and unmarried children under age 21 can accompany the O-1 visa holder in the United States, but they cannot work in U.S.;
• if an O-1 visa worker want to change job, a new visa is necessary.