Nine youths, most in their mid-to-late teens, were arrested in disturbances during and after the Apprentice Boys of Derry parade on Saturday.
Six were arrested for what a PSNI spokesman described as "minor public order offences" during the parade and the three others were arrested during clashes between Catholic teenagers and police officers after the parade.
During those clashes, at Fahan Street in the Bogside area of the city, several petrol bombs were thrown at police officers who earlier in the day had uncovered several dozen petrol bombs in the same area.
In clashes which preceded the annual loyal order parade, more than 50 petrol bombs were thrown by nationalist youths at police in Fahan Street in the Bogside. Two cars were stolen and set on fire during the disturbances.
No one was injured and no arrests were made.
Despite the sporadic but organised violence before and after the parade, the parade itself passed off almost trouble-free.
Seven hundred police officers and 250 marshals from the Apprentice Boys constantly patrolled and monitored the five-mile route of the parade.
Some 10,000 Apprentice Boys accompanied by 120 bands took two hours to complete the parade from the Waterside, across Craigavon Bridge, through the city centre and back to the Waterside.
Most commercial premises along the route of the parade were closed and the police had imposed traffic restrictions in various parts of the city.
Among the official observers were two members of the Parades Commission, including former Portadown Orange man David Burrows who was appointed to the commission in January.