| 1 | DCO | David Crawshaw Consultants Ltd. | | GB | AVCODES |
| 2 | DCO | Distribuidora Y Comercializadora Jaz, S.A. de C.V. | Callsign: Aerojaz, | MEX | AVCODES |
| 3 | DCO | David Crawshaw Consultants Limited | | | ICAO1 |
| 4 | DCO | DIPERT, DAN COACHES | | | SCAC4 |
| 5 | DCOA | DURATRANS CORPORATION | | | SCAC4 |
| 6 | DCOB | DESCON CORPORATION | | | SCAC4 |
| 7 | DCOC | DUNCAN OIL COMPANY INC | | | SCAC4 |
| 8 | DCOG | DKST COMPUTERS | | | SCAC4 |
| 9 | DCOI | DIVERSIFIED CONTROL INC | | | SCAC4 |
| 10 | DCOM | DATAVISION COMPUTER | | | SCAC4 |
| 11 | DCON | Detroit Connecting Railroad Co. | added 1/2004; eliminated 4/2004; 7/2005 | | NAKINA |
| 12 | DCON | DETROIT CONNECTING RAILROAD CO. | | | PWRC |
| 13 | DCON | Detroit Connecting Railroad | | | RSRV |
| 14 | DCON | DETROIT CONNECTING RAILROAD COMPANY | | | SCAC4 |
| 15 | DCOQ | DAYS CORPORATION | | | SCAC4 |
| 16 | DCOU | DOW SILICONES UK LIMITED | | GB | BIC |
| 17 | DCOU | DOW CORNING CORPORATION | | | PWRC |
| 18 | DCOU | Dow Corning Corporation | | | RSRV |
| 19 | DCOU | DOW CORNING LIMITED | | | SCAC4 |
| 20 | DCOZ | DOVER COOP | | | PWRC |
