| Op. ___ (footnote abbr.) | 24 |
| Op. ___ (in the work cited) | 27 |
| Op. ____ (footnote abbr.) | 25 |
| Opaque drinking vessel | 22 |
| Opaque watercolor technique | 27 |
| OPEC member since 1967 | 22 |
| OPEC member, for short | 22 |
| OPEC production cutback? | 24 |
| OPEC's "gold" | 27 |
| OPEC's biggest customer | 27 |
| OPEC's headquarters | 23 |
| OPEC's largest customer | 27 |
| Open a bottle of cheap beer? | 28 |
| Open a compressed file | 22 |
| Open a large container | 22 |
| Open a medicine bottle | 22 |
| Open a prescription bottle | 26 |
| Open a round, in poker | 22 |
| Open a thigh-high boot, maybe | 29 |
| Open a toothpaste tube | 22 |
| Open African grasslands | 23 |
| Open an achievement, e.g. | 25 |
| Open area in the woods | 22 |
| Open areas in the forest | 24 |
| OPEN AT YOUR OWN RISK! | 22 |
| Open audition, in slang | 23 |
| Open by moving a sliding rod | 28 |
| Open center in a structure | 26 |
| Open competitors, often | 23 |
| Open court hearing, in law | 26 |
| Open enough to peep through | 27 |
| Open hearings in courts | 23 |
| Open horse-drawn carriages | 26 |
| Open House in real estate | 26 |
| Open land for an eland | 22 |
| Open mic night participant | 26 |
| Open mic performer, often | 25 |
| Open mike night candidate | 25 |
| Open mike night participant | 27 |
| Open mike night participants | 28 |
| Open military conflicts | 23 |
| Open on Christmas morning | 25 |
| Open oneÂ’s heart, perhaps | 29 |
| Open past legal closing time | 28 |
| Open porch at the inn? | 22 |
| Open railcar used in mines | 26 |
| Open river valley, e.g. | 23 |
| Open shaft for a staircase | 26 |
| Open sign's flip side | 25 |
| Open Society founder George | 27 |
| Open space between buildings | 28 |
| Open space for walking | 22 |
| Open space in a forest | 22 |
| Open space in the woods | 23 |
| Open spaces in a forest | 23 |
| Open spaces in forests | 22 |
| Open spaces in sylvan places | 28 |
| Open spaces in the woods | 24 |
| Open spaces under desks | 23 |
| Open swath in a forest | 22 |
| Open the throttle wide | 22 |
| Open to doubt or debate | 23 |
| Open to suggestions, say | 24 |
| Open two interlocking tabs | 26 |
| Open up, as a jail cell | 23 |
| Open up, as a new shirt | 23 |
| Open up, as some jackets | 24 |
| Open wider, as a pupil | 22 |
| Open with a combination | 23 |
| Open with a paper knife | 23 |
| Open without a corkscrew | 24 |
| Open, as a bolted door | 22 |
| Open, as a bottle of aspirin | 28 |
| Open, as a cabernet sauvignon | 29 |
| Open, as a champagne bottle | 27 |
| Open, as a change purse | 23 |
| Open, as a compressed file | 26 |
| Open, as a court document | 25 |
| Open, as a garment bag | 22 |
| Open, as a large envelope | 25 |
| Open, as a medicine bottle | 26 |
| Open, as a pill bottle | 22 |
| Open, as a screen door | 22 |
| Open, as a sleeping bag | 23 |
| Open, as a toothpaste tube | 26 |
| Open, as a vitamin bottle | 25 |
| Open, as an aspirin bottle | 26 |
| Open, as Christmas presents | 27 |
| Open, as classified records | 27 |
| Open, as shipped goods | 22 |
| Open, as some wine bottles | 26 |
| Open, as to compromise | 22 |
| Open, like some jackets | 23 |
| Open, tartlike pastries | 23 |
| Open, to Shelley or Keats | 25 |
| Open-air gamboling milieu | 25 |
| Open-air gamboling place | 24 |
| Open-air swimming pool | 22 |
| Open-and-shut case spoiler | 26 |
| Open-bodied antique auto | 24 |