synthetic oils and blends with synthetic and petrolium oil

Try this one:

There are clear benefits of using synthetic oil in terms of reduced engine wear, longer change intervals (but do not exceed manufacturer warranty requirements), slightly better fuel economy (one or two tenths of mpg), reducing the likelihood of sludge (in engines that are susceptible to sludge), and easier starting in cold weather. If you plan on selling your car yourself (instead of trade-in), you will likely get more money for the car if you can document your synthetic oil changes.

If you use conventional oil and change it every 5000 miles, and you plan on trading in your car after 3 years or less, then the benefits of synthetics are less clear.

I you change your conventional oil every 3000 miles, or plan on keeping your car for 6 years or more, or plan on selling the car yourself, then using synthetic oil with 5000-6000 mile change intervals will provide substantial benefits over conventional oil at little or no extra cost.

IMO, in the 21st century (please ignore those 20th century oil studies often quoted on this forum), synthetic oil is an absolute no-brainier.