4 prong pigtail, 3 hole 220V outlet?

I'm an electrician, I drive a service truck, if you call me to change the outlet I'm probably not going to do it.

If there are only 3 wires in the box feeding the outlet box the correct safe, cheap, and legal (NEC 250.140 Ex.) method is to change the cord, they are typically less than $20. http://amzn.to/2D81i46 Upgrading the receptacle can be done if you fish a new grounding wire back to a qualified grounding electrode, that can be difficult to do properly, and completely necessary. Generally I don't recommend owners messing with the building, too easy to make deadly mistakes, where the installation instructions for the range (or dryer) will clearly show the correct cord installation method.

Go the website of the oven maker and download the "Installation Instructions". They will tell you how to connect the cord and how to bond the ground to the neutral, here is an example, https://www.homedepot.com/catalog/pdfImages/c8/c88... , see page 4.

A very good short explanation of the older style 3 wire receptacles can be found below, with a picture of a "grounded neutral".

(There's a thumbs down festival going on here, well, except one guy, probably didn't give himself a thumbs down)

You can buy a new 3 prong cord and swap it out. That will require binding the neutral to the ground inside the unit.

Upgrading the a 4 prong outlet is 'preferred' but not required buy code.

Call the oven manufacturer and ask what is the best thing to do so as not to void the warranty on the oven.

The 4 prong plug is required in mobile homes.

They changed the code several years back, adding a ground wire. The old style is acceptable if you only have 3 wires back to breaker box. So, you figure out how many wires you have installed and get a receptacle/plug/adapter that matches. But check the code to be sure. We ran into the same problem a few years back, but had run 4 cables to the stove and used only 3 because that is what the stove had. So, we replace the receptacle from 3 to 4 and used the new stove plug. You might have the same situation. I think the ground wire is smaller than the power cables. And, fooling with those big cables is a pain.

generally the wall outlet is changed in this situation

see instructions that came with oven for converting it to three prong power supply. if they aren't in the instructions, see maker's website online for how to do this safely

A couple options. You can run a 3 prong cord and just run a ground pigtail wire from the neutral post of the stove to the ground point/metal case/chassis of the stove which helps ground the stove chassis in cases of a short to the metal of the stove from the power wires. The problem is that if the neutral path wiring of the circuit goes bad for some reason, then the stove will not be grounded since you only have one neutral wire and you could receive dangerous shocks. That is why the newer codes upgraded to 4 prong/4 wire circuits with a separate ground wire path. That adds another path of protection to ground the appliance in cases of a defect in the neutral wiring.

A cheaper alternative to running all new wiring that I've used is to just run a ground wire from the panel ground bar to the stove outlet and then install a 4 prong outlet ... wire up the outlet as usual with the two hots, neutral and ground and then use the 4 prong plug from the stove. Just run the new ground wire along the existing wiring from the panel to the stove outlet...secure and tape the wire in place along the way....if that is a possible way to do so. Use #6 or 8 gauge solid ground wire...sold in rolls of various lengths at home centers.

Call the oven manufacturer and ask what is the best thing to do so as not to void the warranty on the oven.