In 1991, LEGO released 22 Service Packs sets across 3 subthemes, all of these sets have been retired. Subthemes for that year included Technic, Town, and Trains.
Most valuable 1991 LEGO Service Packs set
5300 Train Motor 9V $127.63
Highest growth 1991 Service Packs set
5154 Decorated Elements +2258.79%
22 sets

5042 Space Light and Radar Plates, Disks and ConesTransparent Lights

Theme Service Packs
Year 1991
Pieces 50
Availability Retired
5042 LEGO Space Light and Radar Plates, Disks and ConesTransparent Lights
Retail $2.49
Value $20.38
Growth  +718.5%
Annual growth 5.4%

5043 Mini Antennas, Control Sticks and Antennas

Theme Service Packs
Year 1991
Pieces 26
Availability Retired
5043 LEGO Mini Antennas, Control Sticks and Antennas
Retail $2.49
Value $25.82
Growth  +936.9%
Annual growth 6.6%

5044 Harbor Base with Slipway

Theme / Subtheme Service Packs / Town
Year 1991
Pieces 3
Availability Retired
5044 LEGO Town Harbor Base with Slipway
Retail $5.89
Value $29.72
Growth  +404.6%
Annual growth 4.9%

5045 Magnets, Magnet Holders

Theme Service Packs
Year 1991
Pieces 12
Availability Retired
5045 LEGO Magnets, Magnet Holders
Retail $1.95
Value $37.05
Growth  +1800.0%
Annual growth 7.5%

5046 Wheels, Tyres and Spring Suspension

Theme Service Packs
Year 1991
Pieces 10
Availability Retired
5046 LEGO Wheels, Tyres and Spring Suspension
Retail $1.49
Value $11.65
Growth  +681.9%
Annual growth 4.7%

5099 Pneumatic Valves

Theme / Subtheme Service Packs / Technic
Year 1991
Pieces 1
Availability Retired
5099 LEGO Technic Pneumatic Valves
Retail $2.25
Value $5.91
Growth  +162.7%
Annual growth 3.1%

5114 Motor 9 V

Theme Service Packs
Year 1991
Pieces 1
Availability Retired
5114 LEGO Motor 9 V
Retail $15.99
Value $23.52
Growth  +47.1%
Annual growth 1.1%

5115 Battery Box 9 V

Theme Service Packs
Year 1991
Pieces 1
Availability Retired
5115 LEGO Battery Box 9 V
Retail $10.99
Value $41.16
Growth  +274.5%
Annual growth 4.0%

5118 Flex System Elements

Theme / Subtheme Service Packs / Technic
Year 1991
Pieces 35
Availability Retired
5118 LEGO Technic Flex System Elements
Retail $5.99
Value $47.17
Growth  +687.5%
Annual growth 6.3%

5153 Plane Accessories

Theme / Subtheme Service Packs / Town
Year 1991
Pieces 23
Availability Retired
5153 LEGO Town Plane Accessories
Retail $4.99
Value $6.46
Growth  +29.5%

5154 Decorated Elements

Theme Service Packs
Year 1991
Pieces 26
Availability Retired
5154 LEGO Decorated Elements
Retail $1.99
Value $46.94
Growth  +2258.8%
Annual growth 5.5%

5155 Sloping Frames, Space Wings, Motors and Seats

Theme Service Packs
Year 1991
Pieces 19
Availability Retired
5155 LEGO Sloping Frames, Space Wings, Motors and Seats
Retail $3.49
Value $14.55
Growth  +316.9%
Annual growth 5.8%

5156 Transparent Bricks

Theme Service Packs
Year 1991
Pieces 17
Availability Retired
5156 LEGO Transparent Bricks
Retail $3.49
Value $25.75
Growth  +637.8%
Annual growth 6.2%

5157 Town and Space Tools

Theme Service Packs
Year 1991
Pieces 32
Availability Retired
5157 LEGO Town and Space Tools
Retail $3.49
Value $23.57
Growth  +575.4%
Annual growth 5.9%

5158 Runway T-Junction and Circle Base Plates

Theme / Subtheme Service Packs / Town
Year 1991
Pieces 2
Availability Retired
5158 LEGO Town Runway T-Junction and Circle Base Plates
Retail $5.99
Value $23.62
Growth  +294.3%
Annual growth 4.1%

5159 Two Straight Airport Runways

Theme / Subtheme Service Packs / Town
Year 1991
Pieces 2
Availability Retired
5159 LEGO Town Two Straight Airport Runways
Retail $5.99
Value $23.43
Growth  +291.2%
Annual growth 4.1%

5164 Hinges, Turntables and Couplings

Theme Service Packs
Year 1991
Pieces 17
Availability Retired
5164 LEGO Hinges, Turntables and Couplings
Retail $2.49
Value $11.34
Growth  +355.4%
Annual growth 4.6%

5165 Hinges, Couplings and Tilting Bearings

Theme Service Packs
Year 1991
Pieces 31
Availability Retired
5165 LEGO Hinges, Couplings and Tilting Bearings
Retail $2.99
Value $10.82
Growth  +261.9%
Annual growth 2.3%

5166 Lamp Holders, Tool Holder Plates

Theme Service Packs
Year 1991
Pieces 18
Availability Retired
5166 LEGO Lamp Holders, Tool Holder Plates
Value $4.77

5271 Tyres and Hubs 49.6 mm White

Theme Service Packs
Year 1991
Pieces 4
Availability Retired
5271 LEGO Tyres and Hubs 49.6 mm White
Retail $2.95
Value $5.14
Growth  +74.2%
Annual growth 2.6%

5272 Cylinder Motor

Theme / Subtheme Service Packs / Technic
Year 1991
Pieces 9
Availability Retired
5272 LEGO Technic Cylinder Motor
Retail $2.99
Value $7.35
Growth  +145.8%
Annual growth 2.9%

5300 Train Motor 9V

Theme / Subtheme Service Packs / Trains
Year 1991
Pieces 3
Availability Retired
5300 LEGO Train Motor 9V
Retail $24.99
Value $127.63
Growth  +410.7%
Annual growth 3.1%