The highway heads south from there for 26 kilometres (16 mi) towards the Canada–United States border before beginning its eastward routing.

[6] It has a short 1.4-kilometre (0.87 mi) long concurrency with the north–south 37 before resuming its eastward routing towards Val Marie.

Access to the West Block of the Grasslands National Park is about 5 kilometres (3.1 mi) south of Val Marie.

Several kilometres east of Val Marie, Highway 18 turns north and enters the Wood Mountain Hills.

It continues south out of the hills where it provides access to the East Block of Grasslands National Park and meets Highway 2 a few kilometres north of the U.S. border.

Along this stretch, Highway 18 provides access to Fife Lake[14] and Rockin Beach Regional Park.

It continues east en route to Estevan providing access to several communities including Gladmar,[18] Lake Alma,[19] Beaubier,[20] Ratcliffe, Oungre,[21] Torquay,[22] and Outram; intersects Highways 28, 707, 35, 606, 350 and 47; and crosses Long Creek and Souris River.

The highway continues east from Bienfait and provides access to multiple communities, such as Hirsch, Frobisher,[25] Oxbow,[26] Glen Ewen,[27] Carnduff,[28] Carievale,[29] and Gainsborough;[30] intersects several highways, including 605, 604, 9, 603, 601, 318, 8, and 600; and crosses the rivers of Moose Mountain Creek, Antler River, and Gainsborough Creek.