More than two years of heated debate on how to value employee stock options has brought many companies full circle — right back to Black-Scholes.

Of 47 chief financial officers who responded to a new survey, 29 said they will continue using the traditional Black-Scholes valuation model when expensing employee stock options. Only 17 said they will switch to the newer binomial lattice model (also known as Cox, Ross, Rubinstein); one respondent planned to use another model. The survey was conducted by Financial Executives International (FEI) and Baruch College.

By June 15, most public companies will be required to implement Statement 123R, the Financial Accounting Standards Board’s revised rule on expensing employee stock options. Private and small companies have until December 15.

FEI president and chief executive officer Colleen Cunningham told CFO.com that she was surprised more finance chiefs didn’t choose the binomial model. Black-Scholes “tends to overestimate” the value of the options, added Cunningham; the binomial model uses more inputs and is generally considered to provide a more accurate estimate.

As for why CFOs may be sticking with Black-Scholes, Cunningham noted that more companies are familiar with that model and already have the attendant procedures and processes in place to value options. At this late date, she added, reworking a company’s internal controls to implement the binomial method might also require additional Sarbox 404 compliance work. A switch in valuation methods would force many compensation committees, who work on stock-option plans late in the year (usually November), to revise plans that have already been approved. And the mid-year implementation of 123R also overlaps with the time when companies are busy preparing their 10-Ks.