Why is Opera moving to WebKit? Because it has to.

Opera is about to shake up its browser business in a major way, by abandoning its Presto rendering engine in favor of the increasingly-ubiquitous WebKit, and by joining in the open-source Chromium project. The Norwegian firm has also announced that it now has more than 300 million monthly users.

Opera had already let slip the shift to WebKit when a company video “leaked” last month depicting a new, WebKit-based Opera browser codenamed Ice that’s going to hit iOS at some point, but the move to the Chromium framework — at the expense of Opera’s own, certainly on the desktop — comes as more of a surprise. I’m going to go out on a limb here, but I think it unlikely that Opera founder Jon von Tetzchner would have let this happen if he still held enough shares to exert influence on the company’s direction.

“300 million marks the first lap, but the race goes on,” CEO Lars Boilesen said in a statement. “On the final stretch up to 300 million users, we have experienced the fastest acceleration in user growth we have ever seen. Now, we are shifting into the next gear to claim a bigger piece of the pie in the smartphone market.”

Compatibility

In order to claim that bigger piece, WebKit is a necessity, Opera CTO Håkon Wium Lie told me on Wednesday morning. After all, that same rendering engine is what underpins Apple’s Safari and Google’s Chrome, and given the dominance of iOS and Android in the mobile market, it’s become a primary concern for web developers.

“People are using WebKit prefixes for CSS properties and it’s been troublesome for other browsers to render those pages without supporting the WebKit prefixes,” Wium Lie said. “That has been part of the shift we’re seeing and it’s also been part of our decision making. What we see as very positive is that we will be able to take some of our best engineers and have them work on common code that many people will use — we will reach more people this way.”

Opera’s statement said WebKit and Chromium would gradually be used in “most of” the company’s upcoming smartphone and PC browser iterations. However, Wium Lie suggested that “our whole product line will be affected in due course by this”.

Those who want to see some competition maintained in the mobile browser rendering engine space had better keep their fingers crossed that Windows Phone gains more traction and that Mozilla’s Firefox OS, which uses Gecko, sells like hotcakes too.

What’s Opera for now?

Chromium, WebKit and Opera have met before, of course, notably last year when Russian web giant Yandex released a browser that combined Chromium with WebKit and Opera’s Turbo engine, which uses server-side compression to cut down on the amount of data the user needs to download, saving them money in the process.

Wium Lie denied that Opera would be paring down its model to that of a mere feature provider, but hinted that there was some precedent in what Yandex did. He also stressed that Turbo and the “impressive infrastructure” that enables it were integral to Opera’s future.

“We will be using Chromium, but you can do a whole lot of stuff on top of that,” he said. “Yandex released a browser that does some interesting things and adds features, and changes the UI, and it’s different from the Chromium browser itself. We worked with Yandex on that and we will be doing similar things with our own stuff. The rendering engine is an important part of the browser -– it’s not everything.”

Opera’s new Android browser will get a showing at Mobile World Congress later this month (we will be there, naturally), where the company will also be touting its operator-targeting, pay-per-use Opera Web Pass technology. As for Ice and the other outcomes of the shift to WebKit and Chromium, we’ll have to wait a bit longer to see what the new Opera looks like.