What: Shares of Criteo SA (ADR) (CRTO 0.28%) were up 19.4% as of 11:00 a.m. ET after the performance marketing specialist released strong fourth-quarter 2015 results.

So what: Quarterly revenue excluding traffic acquisition costs (ex-TAC) climbed 51% year over year (43% at constant currency) to 146 million euros, driven by Criteo's addition of over 900 net clients during the quarter and a client retention rate of over 90%. That translated to 53% growth in adjusted earnings before interest, taxes, depreciation, and amortization (EBITDA) to 49 million euros and 83% growth in adjusted net income to 43 million euros, or 0.66 euros per diluted share.

For perspective, Criteo's guidance provided last quarter called for lower revenue ex-TAC between 134 million euros and 139 million euros and adjusted EBTIDA of 39 million euros to 46 million euros. And analysts, on average, were expecting revenue of 138.2 million euros to result in adjusted earnings of 0.40 euros per diluted share.

CEO Eric Eichmann said:

2015 was another terrific year for us. We crossed the 10,000 client and €1 billion revenue marks while continuing to invest significantly in innovation. I am thrilled to take the helm at such an exciting time and look forward to our 2016 initiatives.

Now what: For the current quarter, Criteo expects revenue ex-TAC between $153 million and $158 million (or between 139 million euros and 144 million euros), and adjusted EBTIDA between $36 million and $41 million (or between 33 million euros and 37 million euros). Analysts' consensus estimates predicted revenue near the lower end of Criteo's guidance range.

For the full fiscal-year 2016, Criteo anticipates revenue ex-TAC to grow between 30% to 34% at constant currency, with adjusted EBITDA margin as a percentage of revenue increasing between 60 and 100 basis points over fiscal 2015. Analysts' consensus estimates called for reported revenue growth -- which are generally higher for Criteo in today's economic environment than constant currency growth expectations -- of 30% in fiscal 2016.

In the end, this was a cut-and-dried case of Criteo significantly outperforming both its own expectations and those of Wall Street, then offering a strong view of the coming year. With shares still down more than 20% year to date and trading at a reasonable (given its growth rates) 22.4 times this year's expected earnings, it's no surprise investors were willing to so aggressively bid up Criteo stock today.