“The Sisters Brothers,” like the Patrick deWitt book on which it’s based, takes a low-key comic approach to the Western genre, with thoughtful performances by Joaquin Phoenix and John C. Reilly as two brothers/assassins/bounty hunters: Charlie Sisters (Phoenix) and Eli Sisters (Reilly).

The humor, however, is so subtle that the audience might not laugh. A case in point: Late in the movie, a fugitive chemist named Hermann Kermit Warm, played by Riz Ahmed, talks of why he’s so intent on finding gold in the rivers of Northern California. He says he dreams of setting up an 1850s socialist utopia — in Dallas.

When that line was uttered at a recent screening at the Toronto International Film Festival, it drew a laugh from a party of one. It might strike a bigger chord in Texas.

In “The Sisters Brothers,” Ahmed’s Warm serves as rabbit, if you will. Everyone is chasing him during the Gold Rush. It turns out that Warm has a chemical formula that you can put in river water to make the gold nuggets visible.

The bigtime bossman named the Commodore (Rutger Hauer) has hired the Sisters brothers to track down Warm so that he can get the formula. Also on Warm’s trail is a fancy-pants but thorough scout, John Morris (Jake Gyllenhaal), who is supposed to help the Sisters brothers find their prey. Morris is the advance man, while the Sisters follow behind by a day or two. And they’re the sort of brothers who get into all sorts of scrapes along the way from Oregon to Northern California, mainly because Charlie is a bigtime drunk who gambles and fights.

The movie plays out like an anti-Western in some ways. You have two brothers on horseback, talking and talking, with the older brother Eli wondering why Charlie has to be so gun-happy. (In flashbacks, you see that the brothers were born in violence ).

Phoenix’s Charlie can be downright scary during his outbursts, but Reilly’s Eli is the revelation here — a thoughtful killer who wonders whether he might ever live a normal, nonviolent life. Charlie thinks he’s a bit loony to dream.

Gyllenhaal has a supporting role as the scout Morris, but he makes the most of it, speaking with high-toned formality as he takes notes about how fast Warm is moving and where he’s headed. There’s something sinister about Morris, but he also has empathy when you least expect it.

Ahmed’s Warm, meanwhile, has an apt last name, because he’s missing the mean bone that’s so much a part of the Sisters brothers.

All of this comes to the big screen under the direction of French auteur Jacques Audiard, whose previous films include “Rust and Bone” and “A Prophet.” Audiard might seem to be an unlikely director of a Western, but he was approached by producers Reilly and Alison Dickey (Reilly’s wife) at the Toronto International Film Festival in 2012. Reilly and Dickey had the rights to the book and thought Audiard would have the right sensibility to approach this quirky Western.

As you’ll see, Audiard does indeed have a fresh perspective, making “The Sisters Brothers” more intimate and less epic that the traditional Western. And although there’s plenty of violence, it’s missing the ironic ultraviolence of a Quentin Tarantino Western as well as the classic, archetypal elements of other Western tales.

It’ll be interesting to see how U.S. audiences respond to this oddity, shot on 35 mm by cinematographer Benoit Debie, who has collaborated with Harmony Korine and Gaspar Noe.

“The Sisters Brothers” is unusual, but it’s a lot of fun if you like low-key laughs.