diff --git a/src/bin/commands/trimmer.rs b/src/bin/commands/trimmer.rs
index 03befa6..ccc3693 100644
--- a/src/bin/commands/trimmer.rs
+++ b/src/bin/commands/trimmer.rs
@@ -50,6 +50,18 @@ pub(crate) struct TrimmerOpts {
     #[clap(long, short = 'L', default_value = "15")]
     filter_longer: usize,
 
+    /// Size of window to look for oscillations.
+    #[clap(long, default_value = "15")]
+    osc_window: usize,
+
+    /// Number of oscillations in a window to trigger trimming/masking.
+    #[clap(long, default_value = "4")]
+    osc_max_oscillations: usize,
+
+    /// Difference between adjacent bases to be considered on oscilation.
+    #[clap(long, default_value = "10")]
+    osc_delta: usize,
+
     /// Minimum difference in base-quality for one read to correct an overlapping
     /// base from the other read.
     #[clap(long, short = 'd', default_value = "15")]
@@ -149,7 +161,24 @@ impl Command for TrimmerOpts {
                         }
                     }
                     Operation::Osc => {
-                        unimplemented!("OSC not implemented")
+                        if let Some(i) = base_quality::identify_trim_point(
+                            r1.qual(),
+                            self.osc_delta as i32,
+                            self.osc_window,
+                            self.osc_max_oscillations,
+                        ) {
+                            // TODO [Brent]: allow clip or mask with flag
+                            base_quality::clip_read(&mut r1, 0usize..i);
+                        }
+                        if let Some(i) = base_quality::identify_trim_point(
+                            r2.qual(),
+                            self.osc_delta as i32,
+                            self.osc_window,
+                            self.osc_max_oscillations,
+                        ) {
+                            // TODO [Brent]: allow clip or mask with flag
+                            base_quality::clip_read(&mut r2, 0usize..i);
+                        }
                     }
                     Operation::LenFilter => {
                         if r1.seq().len().min(r2.seq().len()) < self.filter_shorter
diff --git a/src/lib/base_quality.rs b/src/lib/base_quality.rs
index 8397a61..6afd974 100644
--- a/src/lib/base_quality.rs
+++ b/src/lib/base_quality.rs
@@ -3,8 +3,48 @@ use seq_io::fastq::OwnedRecord;
 
 use std::ops::Range;
 
-pub fn find_oscillating_quals(_bqs: &[u8]) -> Range<usize> {
-    unimplemented!("find_oscillating_quals");
+/// Returns an optional point at which to trim the read due to quality oscillations.
+///
+/// # Arguments
+///
+/// * `quals` - The quality scores for the read.
+/// * `osc_delta` - The minimum difference in quality scores to be considered an oscillation.
+/// * `window_size` - The number of bases to consider in a window.
+/// * `max_oscillations` - The maximum number of oscillations allowed in a window.
+pub fn identify_trim_point(
+    quals: &[u8],
+    osc_delta: i32,
+    window_size: usize,
+    max_oscillations: usize,
+) -> Option<usize> {
+    // Compute a vector of booleans to represent whether each position is immediately
+    // after an oscillation
+    let mut is_osc = vec![false; quals.len()];
+
+    for i in 1..quals.len() {
+        is_osc[i] = (quals[i] as i32 - quals[i - 1] as i32).abs() >= osc_delta;
+    }
+
+    // TODO [brent]: this is ~O(n^2/2) and could be ~O(n)
+    // instead, convert is_osc into a vector of indices of oscillations. then can use a
+    // window of `max_oscillations` and check if there are at least `window_size` oscillations in the window.
+    for i in 1..is_osc.len() {
+        if !is_osc[i] {
+            continue;
+        }
+        let mut n = 1;
+        #[allow(clippy::needless_range_loop)] // will refactor this later anyway
+        for j in (i + 1)..std::cmp::min(i + window_size, quals.len()) {
+            if is_osc[j] {
+                n += 1;
+                if n > max_oscillations {
+                    return Some(i);
+                }
+            }
+        }
+    }
+
+    None
 }
 
 // Indicates which tail(s) to clip.
@@ -82,4 +122,41 @@ mod tests {
         let range = find_high_quality_bases(bqs, 'I' as u8, 1, Tail::Right);
         assert_eq!(range, 0..bqs.len() - 1);
     }
+
+    #[test]
+    fn test_identify_trim_point() {
+        let quals = vec![33; 100];
+        let oscillation = 10;
+        let window_size = 20;
+        let max_oscillations = 3;
+
+        let trim_point = identify_trim_point(&quals, oscillation, window_size, max_oscillations);
+
+        assert_eq!(trim_point, None);
+    }
+
+    #[test]
+    fn test_identify_trim_point_not_quite_big_enough_changes() {
+        let base = [9u8, 18, 27, 36, 27, 18];
+        let quals: Vec<u8> = base.into_iter().cycle().take(base.len() * 20).collect();
+
+        let oscillation = 10;
+        let window_size = 20;
+        let max_oscillations = 3;
+
+        let trim_point = identify_trim_point(&quals, oscillation, window_size, max_oscillations);
+        assert_eq!(trim_point, None);
+    }
+
+    #[test]
+    fn test_identify_trim_point_finds_point() {
+        let left = vec![30u8; 50];
+        let right = [15u8, 22, 35, 20, 32];
+        let quals =
+            [&left[..], &right.into_iter().cycle().take(right.len() * 5).collect::<Vec<u8>>()]
+                .concat();
+
+        let trim_point = identify_trim_point(&quals, 10, 20, 3);
+        assert_eq!(trim_point, Some(50));
+    }
 }