does filling up a gas tank in Spain require a credit card with pin?

I haven’t had much luck with at pump purchases when using my U.S. credit card and have stopped trying. The exception was at Costco, Getafe, outside of Madrid. I go to stations where I pay inside after pumping and have never had an issue. No PIN. Most stations are contactless payment, but for some you still need to insert the card.

Some places yes, some places no. I've had to resort to my Schwab Bank debit card with PIN occasionally, but elsewhere had no problem with tap to pay.

If the pump has been updated to "tap to Pay" then chances are good you will be OK, though you would need to keep the total under 50 euro. Possibly with Apple/Google Pay, higher amounts will be OK. Sometimes, if you keep the purchase below some magic amount, a standard card may go through without a PIN.

Best is to plan fueling up when you can go to a station with a manned pay counter.

Many unmanned automatic pumps require card with PIN, some don't. But if you go outside of closing hours when there is personnel in the shop you can pay in person using a credit card without PIN (before or after pumping). Cash works in many automatic pumps as well. Just try to pump during working hours on weekdays and some human will be there to take your card payment. Your Debit card with PIN should work however.

In Spain, as in most EU countries, the use of chip-and-PIN cards is universal. All card transactions require this type of credit or debit card.

Under current rules, based on the EU Payment Services Directive 2 (PSD2), contactless card payments can usually be made without entering a PIN for transactions up to €50.

However, the terminal must require the PIN when either of these limits is reached:

• €150 or more in accumulated contactless purchases since the last PIN entry, or
• More than 5 consecutive contactless transactions without entering the PIN.

Just pay at the kiosk, not at the pump