The running of the bulls is the central and most famous event of the festival of San Fermin in Pamplona.  The run starts at 8am sharp, every morning of the festival (July 7-14).  There are six bulls and two groups of oxen (steers), easily recognisable by the bells around their necks.  Eight oxen run with the bulls and three are released two minutes later to catch any straggling bulls.  Joining these 17 beasts are thousands of runners wearing white with red handkerchiefs.  Many of the runners carry rolled-up newspapers to gauge distances with the bulls.

Invocation to San Fermin

Just minutes before the run (7:55am), local runners sing an invocation to San Fermin, the patron of the run.  They sing three times: “A San Fermín pedimos (We ask of San Fermin)/ por ser nuestro patrón (for he is our patron)/ nos guíe en el encierro (to guide us in the Bull Run)/ dándonos su bendición (giving us his blessing)”. They end by shouting “Viva San Fermín!, Gora San Fermín!” (Long live San Fermin! — First in Spanish, then in Basque)

The rockets

Exactly at eight o’clock in the morning, the bang of a rocket announces the opening of the bull pens. A second rocket goes off immediately when all six bulls are on the loose. When the encierro is over, and all the bulls have reached the Plaza de Toros, a third rocket is fired.

The bulls run up the hill of Santo Domingo towards the Plaza del Ayuntamiento (City Hall). They cross the square onto Mercaderes street, and then enter Calle Estafeta, the longest stretch of the run.  At the end of Estafeta, the herd rounds the Telefónica bend and charges through the callejón, the alley that leads into the bullring; the dobladores then guide the bulls into their chiqueros, or boxes.

via Click here for all the information you could need – Fiestas de San Fermín 2009.