I know this is a basic question but since I'm planning an transatlantic trip I want to be sure to get it right and not be tripped up by missing something in fine print. According to CO.com, "Earn OnePass miles with standard fares on Delta Air Lines-operated flights, with the following general exceptions: all free travel, industry-free or industry-reduced rate tickets, charter flights and promotional certificates. To receive mileage credit, present your OnePass number when you make reservations or check in for your flight." This means that I can book the flights directly with Delta and still receive EQMs, correct? Thanks.

I've done this a few times, and you have to be careful to make sure your CO number is on your ticket stub. Since Delta doesn't make it easy to apply another airlines number, like CO and NW do, you can't, or at least I haven't, had luck getting my CO number on from home. However, if you check in at the delta kiosk at the airport you can do it there. If not available do it at the ticket counter, or in the case where my first leg was on NW ask the gate agent to apply your CO number.
The other gottcha is class of service. L, U and T only get 50% EQMs.
The good is that your miles post very quickly, much quicker than if you fly on CO or NW. Normally within a couple of days if not the day of your flight.
This is the one thing DL has done right for many years.

thanks for the reply

Last year I travelled on Delta and booked on Delta.com. When I arrived at the airport I asked the agent at the ticket counter to enter my Continental number. Even though I had received a boarding pass when I arrived at the gate the I was being paged. My reservation had been cancelled when the ticket counter tried to enter my One Pass number. The gate agent re-instated the reservation, and had not yet given away my seat assignment.

Save the original boarding pass because the miles never posted with Continental and CO demanded the original boarding passes, which took months for me to find becaues they were lost in the two hurricanes which hit us in Florida. During hurricane preparation I gathered all papers and documents and sealed them in large heavy duty trash bags to protect against water damage from the hurricane. It took months before the documents were sorted and re-filed back to the normal locations and I eventually ran across the boarding passes.