Bulgaria
| Country: | Bulgaria |
| Type: | Postage stamps |
| Series: | Undersea research in the Black Sea |
| Nominal: | 18 ст |
| Year: | 1973 |
| Perforation: | line 12½ |
| Mintage: | 180,000 |
Undersea research in the Black Sea
 Diver 0.06$ |  Underwater House ”Shelf 1” 0.08$ |  Camera Lift "NJW 100" |  Lifting Balloon |
 Divers |  Underwater House ”Shelf 1” |  Camera Lift "NJW 100" |  Lifting Balloon |