That said, generally speaking, a 2002 Ford Focus would likely benefit from:
* Conventional oil: This is usually the most affordable option, and may be perfectly suitable if you do shorter drives and/or change your oil frequently (every 3000-5000 miles).
* Synthetic blend oil: This is a middle ground between conventional and fully synthetic oils. It provides better performance and longer life than conventional oil but at a lower cost than fully synthetic. This is a good choice for many drivers.
* Fully synthetic oil: This is the best performing oil, offering superior protection and longer drain intervals (often 7500-10,000 miles or more). However, it is also the most expensive.
Regarding the viscosity (weight) of the oil: Your owner's manual will specify the recommended viscosity grade, often something like 5W-30 or 10W-30. Using the wrong viscosity can harm your engine.
In short: Check your owner's manual! It's the only definitive source for the correct oil type and viscosity for your specific 2002 Ford Focus. Ignoring this could lead to engine damage.
