The visits to the county clerk's office are an annual event during National Freedom to Marry Week, which was created in 1999 by Lambda Legal, a gay rights advocacy law firm.
But this year's event comes just a week after a historic decision by the 9th U.S. Circuit Court of Appeals that found California's ban on same-sex marriage to be unconstitutional.
About 30 people organized by Marriage Equality USA gathered on the Polk Street steps of City Hall, with some holding signs reading, "We all deserve the freedom to marry." One message was written on a red heart-shaped sign decorated as a valentine.
Moving inside the building, about a dozen of those people, including a guitarist, made a slow procession to the clerk's office, as the Oakland East Bay Gay Men's Chorus accompanied them with song.
The lead couple in the procession presented two heart-shaped boxes of chocolates to the clerk's office, and the group sat in a circle on the office's floor, singing a modified version of "Chapel of Love," replacing "chapel" with "courthouse."
Edward Mendoza, 50, who has participated in Marriage Equality's "Marriage License Counter Action" in previous years, said that the court's decision has cast a different tone over the event.
"This year definitely feels like a year of victory," he said outside the clerk's office.
Mendoza, who is bisexual, said he supports marriage equality for everyone. He and his wife married in 1991.
Sheriff's deputies arrived to clear out the cramped office at about 9:50 a.m. Those who failed to follow their orders to disperse were detained.
Sheriff's department spokeswoman Susan Fahey confirmed that eight people were detained for failure to disperse and were later released.
Fewer than 10 minutes later, business as usual resumed at the clerk's office, with heterosexual couples queuing up outside the office to obtain their marriage licenses.
The blushing brides holding fresh bouquets were unaware of the demonstration immediately prior to their arrival.
Marriage Equality USA organized Valentine's Day gatherings at local clerks' offices around the Bay Area and throughout the country, according to the organization.