The costs are being paid by taxpayers.
In late March, Gibson Dunn released a 360-page report based on 75 interviews that found Christie played no role in the lane closures, which jammed traffic in Fort Lee.
The report laid blame on two former Christie allies, both of whom the firm was unable to interview: now-fired Christie aide Bridget Kelly, who penned the infamous "Time for some traffic problems in Fort Lee" e-mail, and a former official of the Port Authority of New York and New Jersey, David Wildstein.
The firm also investigated and dismissed allegations by Hoboken Mayor Dawn Zimmer, who had accused Christie's administration of tying Hurricane Sandy aid to approval of a redevelopment deal.
Lawyers with the firm also have been responding to subpoenas. The invoices list tasks that refer to reviewing and redacting documents.
Also on Friday, the state released invoices from firms representing state employees who have received subpoenas related to the closures, which have been under review by state lawmakers and the U.S. Attorney's Office. The invoices totaled more than $670,000. The names of employees are redacted from the invoices.
The legislative committee investigating the lane closures also has lawyers billing the state, at a cost of more than $700,000 through March.