All the contracts are local. Some contracts state oilers are at the discretion of the employer, some are spelled out in the contract by weight of the crane, or number of axles, or boom length. You can find most of the contracts online:
An Oiler or Fireman or Second Engineer will be employed at the discretion of the Employer. from
https://www.dol.gov/olms/regs/compliance/cba/pdf/2015/private/9031.pdf Albany
Crane Assistant Engineer/Oiler shall be required on all friction Truck Cranes 50 tons and over and Truck Cranes and All Terrain Cranes that are over 60 tons. All Rough Terrain Cranes and Hydraulic Boom Crawler Cranes over 100 tons shall require an assistant engineer.
https://d1jbk5omxb4scq.cloudfront.n...ginal/OE_Local_302_2015_-_2018.pdf?1443538565
All Hydraulic Cherry Picker type machines of over one hundred ten thousand (110,000) pounds gross vehicle weight shall require an Engineer and Oiler and/or Apprentice as the case may be.
http://fvagc.org/wp-content/uploads/2015/05/OEBldg13-171.pdf
No one but an Operating Engineer shall move (drive) the truck crane except where an Oiler or Apprentice is also employed. Where a truck crane of twenty (20) ton lifting capacity or over is used, an Oiler or Apprentice shall also be employed,
http://c.ymcdn.com/sites/mi-ita.site-ym.com/resource/resmgr/Labor/UNDERGROUNDOperatingEngineer.pdf
17.4.1.c Cranes shall be rated at the highest capacity and shall not be derated for the purpose of utilizing the only one (1) Operating Engineers.
17.4.1.d Hydraulic Cranes: Crews on all hydraulic truck mounted cranes of forty (40) ton or larger shall consist of an Operator and it shall require an Assistant to the Operator (Oiler).
17.4.1.e Hydraulic Truck Cranes: Fifty (50) ton and under with factory manufactured remote controls, which allow the crane to be operated and driven on the jobsite from the same seat and the same set of controls and used for hook work only shall not require an Assistant to the Operator. When remote controls are inoperative an Assistant to the Operator (Oiler) is required.
17.4.1.f Hydraulic Boom Crawler Cranes: One hundred (100) ton and under used for hook work only shall not require an Assistant to the Operator. If any attachments are used, including but not limited to, pile driver, draglines, clamshells, suspended equipment, or workers, etc., crews shall consist of an Operator and shall require an Assistant to the Operator (Oiler).
17.4.1.g Hydraulic Boom Crawler Cranes: One hundred (100) ton and over, crews shall consist of an Operator and shall require an Assistant to the Operator (Oiler).
17.4.1.h Rough Terrain Cranes: Up to and including one hundred thirty one (131) ton when used for hook work only shall not require an Assistant to the Operator. If any attachments are used, including but not limited to, pile driver, draglines, clamshells, suspended equipment, or workers, etc., crews shall consist of an Operator and shall require an Assistant to the Operator (Oiler).
17.4.1.i Rough Terrain Cranes: One hundred thirty two (132) ton and over, crews shall consist of an Operator and shall require an Assistant to the Operator (Oiler). AGC-Operating Engineers Local 701 Master Labor Agreement 2015-2019 Page 33
17.4.1.j Boom Trucks: Sixty five (65) ton and under used for hook work only shall not require an Assistant to the Operator (Oiler). If any attachments are used, including but not limited to, pile driver, draglines, clamshells, suspended equipment, or workers, etc., crews shall consist of an Operator and shall require an Assistant to the Operator (Oiler).
17.4.2 Lattice Boom Cranes: Crews on all track or truck cranes and/or similar equipment thirty ton (30) and over shall consist of an Operator and shall require and Assistant to the Operator (Oiler).
from
https://www.agc-oregon.org/wp-content/uploads/2011/10/OE-Final.pdf
That's just a couple examples--
I think a oiler with a twenty ton capacity truck crane is a little too much help, a 120 ton rt by yourself is probably a little much in the other direction. Another contract I read did it by axles- any cranes with only three axles= no oiler,- 4 axles= oiler. I found the rule about factory controls in the upper, not requiring a oiler to be interesting. I've seen that a lot in cranes for sale in california. A lot of used rigs there will have a set of upper driving controls, and always figured they were special ordered for setting precast wall panels, where they were doing a lot of moving, seems it was more to comply with the oiler rules.
I tend to send the manpower required to do the job. I go to jobs all the time with my tms 300 by myself. But the other day doing manbasket work in the blind, I took along a signal man. I took along a extra man this week with one of the 25 tons, because of poor site access. Always take someone with me with my 70 ton. If its a multi day and not much moving of the crane, I'll have just the crane and operator there. I do find it interesting reading the different contracts.