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What: Shares of Barrett Business Services (NASDAQ:BBSI) soared on Wednesday after it reported stellar earnings after the market close on Tuesday. Barrett was up as much as 17% in late afternoon trading.

So what: Barrett, a provider of human resource management services via dozens of branches concentrated mainly in the western United States, blew past analyst estimates for both revenue and earnings when it reported its fourth-quarter results. Net revenue grew 21% year-over-year, and net income jumped 27%. Adjusting for a one-time tax item, EPS came in at $1.17 per share, beating analyst estimates by about 12%.

This growth was driven by both same-store sales growth of 9% as well as a gain in the number of clients. Barrett added 167 net new clients during the quarter, coming in at the high end of its expectations. Guidance for 2015 was also very strong, with gross revenue expected to grow by 18%, again driven by both same-store sales growth and new clients. EPS is expected to grow to $3.30 in 2015. During 2014, an issue related to the company's self-insured workers' compensation reserve led to a net loss of $3.78 per share for the full year.

Now what: Barrett appears to be firing on all cylinders, and the stock now trades at about 10 times the company's expected 2015 earnings even after the surge in the stock price today. However, serious criticism of Barrett's business model related to its handling of reserves first emerged late last year, and it's unclear whether additional reserve-related losses will occur going forward. As always, investors should thoroughly research any company before considering an investment.