Staffing Industry Analysts estimates statement-of-work consulting to be worth $498 billion globally, roughly 13.5% of the total $3.68 trillion in contingent workforce spend in 2017. The US accounts for about half of that, at $246.0 billion spent on SOW projects in 2017. The rest is divided among Europe, with $139.1 billion; the Asia Pacific region, at $49.2 billion; and the rest of the world, for $63.6 billion.

This includes full-time salaried employees of consulting firms, though they may not themselves feel as though they are contingent workers. But because they go from a temporary project with one client to a project with another, these consultants are part of a client’s contingent
workforce and are increasingly managed as such via managed service programs.

Source: The Global Gig Economy 2018