On the Oasis of the Seas, you'll be fine with a shirt and tie. I don't like taking a jacket unless I have to because of weight, so I very often just wear a tie and never have any problems.
__________________ 46 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!
Hi Ven, Just remember, the daily dress code is for dinner in the MDR...If you choose to use an alternative place to eat, like the buffet, you can wear more casual clothes...We found the dinner in the Windjammer Market Place to be just as good and the service was excellent and it took half the time.
Yes, there are "guidelines" in the dining room, but I have never seen them enforced. You will literally see everything from suits to shorts. Its really up to you what you want to wear. You may get a few "looks" if you dont dress to a "T" but its your cruise too, wear what you are comfortable with.