The first privatised incarnation of ScotRail inherited a 46-strong fleet which continued in service.
Following the introduction of newly built Class 170 Turbostar units on primary express services in 1999, the Class 158 fleet was reduced in number by six, with those remaining cascaded away to secondary routes such as the Far North Line.

In 2003, plans existed for part of the fleet to be swapped with Class 156 units operated by Central Trains, as the latter were thought better suited to some of the short-distance routes now being operated by ScotRail's 158s.
However, this failed to materialise and by the mid-2000s operations of the ScotRail 158s ranged from short hops (such as Glasgow Queen Street to Anniesland) to rural lines and long-distance expresses, supplementing other express units.
In 2010 these units started to appear at Glasgow Central station to run on the Glasgow Central to Edinburgh via Shotts line, and on to the Glasgow Central to Whifflet line.
Some additional units have since been acquired from other operators to provide extra capacity.

Refurbishment and reliverying has also taken place since privatisation.
The original ScotRail franchise applied its own livery to the Class 158s, followed by a further repaint by First ScotRail after it took control of the franchise.
The fleet has now gained a permanent blue-and-white livery based on the Scottish Saltire, after Transport Scotland announced in September 2008 that it was specifying a permanent livery for all Scottish trains, which would not be changed in the event of a change of franchisee.
Interiors have also seen attention on more than one occasion.
The most recent refurbishment of 25 units involved repainting, new seating, extra luggage space and new customer information systems.
Toilet retention tanks were also fitted.

In 2018, the additional 8 units acquired by Scotrail from other TOCs were transferred to Northern in stages - the first two occurring in February 2018 and the remainder in December 2018.

Several of the ScotRail units have had names attached - for example 158702 is named BBC Scotland - 75 Years, 158707 is named Far North Line - 125th Anniversary, 158715 is named Haymarket and 158720 is named Inverness and Nairn Railway - 150 Years.
The first privatised incarnation of ScotRail inherited a 46-strong fleet which continued in service. Following the introduction of newly built Class 170 Turbostar units on primary express services in 1999, the Class 158 fleet was reduced in number by six, with those remaining cascaded away to secondary routes such as the Far North Line.
In 2003, plans existed for part of the fleet to be swapped with Class 156 units operated by Central Trains, as the latter were thought better suited to some of the short-distance routes now being operated by ScotRail's 158s. However, this failed to materialise and by the mid-2000s operations of the ScotRail 158s ranged from short hops (such as Glasgow Queen Street to Anniesland) to rural lines and long-distance expresses, supplementing other express units. In 2010 these units started to appear at Glasgow Central station to run on the Glasgow Central to Edinburgh via Shotts line, and on to the Glasgow Central to Whifflet line. Some additional units have since been acquired from other operators to provide extra capacity.
Refurbishment and reliverying has also taken place since privatisation. The original ScotRail franchise applied its own livery to the Class 158s, followed by a further repaint by First ScotRail after it took control of the franchise. The fleet has now gained a permanent blue-and-white livery based on the Scottish Saltire, after Transport Scotland announced in September 2008 that it was specifying a permanent livery for all Scottish trains, which would not be changed in the event of a change of franchisee. Interiors have also seen attention on more than one occasion. The most recent refurbishment of 25 units involved repainting, new seating, extra luggage space and new customer information systems. Toilet retention tanks were also fitted.
In 2018, the additional 8 units acquired by Scotrail from other TOCs were transferred to Northern in stages - the first two occurring in February 2018 and the remainder in December 2018.
Several of the ScotRail units have had names attached - for example 158702 is named BBC Scotland - 75 Years, 158707 is named Far North Line - 125th Anniversary, 158715 is named Haymarket and 158720 is named Inverness and Nairn Railway - 150 Years.
British Rail Class 158