costs 7,85 € for 1 zona (area) in 2010
for maps of the Public Transportation network in Barcelona, see www.tmb.cat
T-10 is the most popular bus-underground-ferrocarrils ticket. It is worth 10 travels within Barcelona (in case of T10 for Area or zona 1) and allows you to switch between bus, metro and ferrocarrils at no extra charge within 1h and 15 minutes from the moment you validate the travel. It can be used by different people travelling together – in this case, you have to remember that the "switching right" will only apply to the last travel validated.
UPDATE 2014: T-10 price has raised to 10,30€ for 1 zona.