However, generally speaking, a conventional or synthetic blend 5W-30 motor oil meeting the specifications listed in your owner's manual is a safe bet. Many reputable brands like Mobil 1, Castrol, Valvoline, Pennzoil, and Quaker State offer oils that would be suitable.
Do not solely rely on this response. Consult your 2005 Ford Focus owner's manual. It will specify the exact weight and type of oil recommended by Ford for your specific engine and driving conditions. Ignoring the manufacturer's recommendations can void your warranty (if applicable) and potentially damage your engine.