Go to http://www.renfe.es/index_mapa.html

Click on "regionales"

Click on cataluna from the dropdown menu

From the top box click Salou to Barcelona

Trains at 07 07, 08 37, 10 13, 11 38 (last one is €5.20 otherwise €6 each way) Several stations in Barcelona, so get a map for the return. (Click on second column - Recorrdio tripo tren - to see the stops for each train) and click on "Seleccionar trenes del trayecto inverso : BARCELONA (*)- SALOU" at the bottom for return times

Change at St Vincenc de Calders (€2.55 each way) to get on the Barcelona local system (€13.55 for a full day ticket) - westernmost station on the map at http://www.renfe.es/cercanias/barcelona/mapa_zonas.html