When I am booking a flight to Europe, I get lots of great airlines then see that the "flight is operated by xx" and I go crazy. Does this mean it is the very tight quarters usually used by United, AA, Delta, or the configuration of the specific airline I am looking for (i.e. Lufthansa, KLM etc)?
Thanks for your help.

The physical aircraft will be one from 'xxx.' So, for example, a United flight "operated by LH" will be marketed by United (they take your money) but the physical craft will be a Lufthansa one.

It means it is a codeshare flight operated by the xx airlines own hardware. You can go to that airlines own site and check out what type of plane it will be.

Unfortunately it is always a Lufthansa flight operated by United, or KLM operated by Delta, so does that mean the super tight seats of United/Delta? Site gives the aircraft but not sure which one to check on seatguru.

In those two examples you would check United and Delta respectively.

<i> Site gives the aircraft but not sure which one to check on seatguru.</i>

Check by flight number and date.

I was just ready to post regarding Lufthansa operated by United. I have not flown with this "arrangement" for a long time, so is all communication now UAL? I am guessing we just disregard LH and go to UAL counter. Too bad if I am right. Thanks

You always go to the <i>operating</i> airline's check-in counters etc., and look at seat maps on that airline's website or on SeatGuru.

I always go into Flight Aware to check flight (if I am traveling in the future, it helps familiarize trip)and it gives type of craft, history of flight ontime record, food service, gates and terminals, scheduled departure etc. Also, change to earthview to check weather

"Super tight"? I've flown Delta, AF and KLM across the Atlantic and noticed no particular difference in seat widths. That's economy, of course, and international versus US routes. You can find more KLM-operated flights into Amsterdam, more Lufthansa flights into Frankfurt.

All seats in economy will be somewhat tight. You can pay a little over $100 for Economy Plus for a little more legroom.

Be glad you're flying Lufthansa or KLM or other airlines. I'm flying United in 10 days, and I've read horror stories about them running their own overseas routes.

If you are on an LH-operated flight, you check in with LH, regardless of how you book your tickets and whether you get a LH or UA flight number.

The only case when a major European airline is handled "mostly" by a US one is KLM around late-90s to early-00's when it was partnered with Northwest, before KL was merged with Air France and NW merged with DL.