diff --git a/ta_lib/volume/src/lib.rs b/ta_lib/volume/src/lib.rs
index cb70ceb2..cc819733 100644
--- a/ta_lib/volume/src/lib.rs
+++ b/ta_lib/volume/src/lib.rs
@@ -1 +1,2 @@
+pub mod vo;
 pub mod vwap;
diff --git a/ta_lib/volume/src/vo.rs b/ta_lib/volume/src/vo.rs
new file mode 100644
index 00000000..3d5567c4
--- /dev/null
+++ b/ta_lib/volume/src/vo.rs
@@ -0,0 +1,39 @@
+use overlap::ema::ema;
+
+pub fn vo(source: &[f64], short_period: usize, long_period: usize) -> Vec<Option<f64>> {
+    let vo_short = ema(source, short_period);
+    let vo_long = ema(source, long_period);
+
+    vo_short
+        .iter()
+        .zip(&vo_long)
+        .map(|(&short, &long)| match (short, long) {
+            (Some(short), Some(long)) => Some(100.0 * (short - long) / long),
+            _ => None,
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_vo() {
+        let source = vec![1.0, 2.0, 3.0, 2.0, 1.0];
+        let expected = vec![None, None, Some(13.5802), Some(2.83224), Some(-10.71604)];
+        let epsilon = 0.001;
+
+        let result = vo(&source, 2, 3);
+
+        for i in 0..source.len() {
+            match (result[i], expected[i]) {
+                (Some(a), Some(b)) => {
+                    assert!((a - b).abs() < epsilon, "at position {}: {} != {}", i, a, b)
+                }
+                (None, None) => {}
+                _ => panic!("at position {}: {:?} != {:?}", i, result[i], expected[i]),
+            }
+        }
+    }
+}