P-R
| Pactolus | pækˈtoʊləs | From the river Pactolus in Anatolia | |
| Padargus | pəˈdɑrɡəs | ||
| Palamnus | pəˈlæmnəs | ||
| Parcae | ˈpɑrsiː | ||
| Peneus | piːˈniːəs | Runs EW through Hellas | From the Peneios river in the Peloponnesus of Greece |
| Permessus | pɛrˈmɛsəs | ||
| Pierius | paɪˈiːriəs | E to W: connects Copaïs Palus and Arethusa Lacus | |
| Phasis | ˈfeɪsɨs | N to S: connects Phoenicis Lacus and Aonius Sinus | |
| Phison | ˈfaɪsɒn | N to S: connects Coloë Palus to Sinus Sabaeus | From Pishon, one of the four rivers of Eden |
| Phlegethon | ˈflɛdʒɨθɒn | From the Phlegethon, a mythical river of Hades | |
| Protonilus | ˌprɒtoʊˈnaɪləs | E to W: connects Coloë Palus and Ismenius Lacus | Means "first Nile" |
| Psychrus | ˈsaɪkrəs | ||
| Pyramus | ˈpɪrəməs | S from pole via Copaïs Palus to junction of Boreosyrtis and Cadmus canals | |
| Pyriphlegethon | ˌpɪrɨˈflɛdʒɨθɒn | NW to SE: connecting Propontis and Lacus Phoenicis | From Pyriphlegethon ("fiery Phlegethon"), a mythical river of Hades |
| Python | ˈpaɪθɒn | From the monster Python which Apollo killed | |
| Rha | ˈreɪ | From a classical name for the river Volga | |
| Rhyndacus | ˈrɪndəkəs | From the classical river Rhyndacus in Anatolia |
Read more about this topic: List Of Martian Canals