diff --git a/dive.c b/dive.c
index 5a10af595..1a9bdd97a 100644
--- a/dive.c
+++ b/dive.c
@@ -594,6 +594,32 @@ static struct event *find_previous_event(struct divecomputer *dc, struct event *
 	return previous;
 }
 
+/* mark all tanks that we switch to in this dive computer's data as used */
+static void mark_used_tanks(struct dive *dive, struct divecomputer *dc)
+{
+	struct event *ev = get_next_event(dc->events, "gaschange");
+	// unless there is a gas change in the first 30 seconds we can
+	// always mark the first cylinder as used
+	if (!ev || ev->time.seconds > 30)
+		dive->cylinder[0].used = true;
+	while (ev) {
+		int idx = get_cylinder_index(dive, ev);
+		dive->cylinder[idx].used = true;
+		ev = get_next_event(ev->next, "gaschange");
+	}
+}
+
+/* walk all divecomputers to find the unused tanks in this dive */
+static void check_for_unused_tanks(struct dive *dive)
+{
+	int i;
+	struct divecomputer *dc;
+
+	for_each_dc(dive, dc) {
+		mark_used_tanks(dive, dc);
+	}
+}
+
 static void fixup_surface_pressure(struct dive *dive)
 {
 	struct divecomputer *dc;
@@ -879,7 +905,7 @@ struct dive *fixup_dive(struct dive *dive)
 	fixup_duration(dive);
 	fixup_watertemp(dive);
 	fixup_airtemp(dive);
-
+	check_for_unused_tanks(dive);
 	for (i = 0; i < MAX_CYLINDERS; i++) {
 		cylinder_t *cyl = dive->cylinder + i;
 		add_cylinder_description(&cyl->type);
diff --git a/dive.h b/dive.h
index ccba7a09f..2b69c949c 100644
--- a/dive.h
+++ b/dive.h
@@ -145,6 +145,7 @@ typedef struct {
 	struct gasmix gasmix;
 	pressure_t start, end, sample_start, sample_end;
 	depth_t depth;
+	bool used;
 } cylinder_t;
 
 typedef struct {
diff --git a/pref.h b/pref.h
index 37beb8faa..e3f0a545a 100644
--- a/pref.h
+++ b/pref.h
@@ -37,6 +37,7 @@ struct preferences {
 	short unit_system;
 	struct units units;
 	short show_sac;
+	bool display_unused_tanks;
 };
 enum unit_system_values { METRIC, IMPERIAL, PERSONALIZE };
 
diff --git a/qt-ui/mainwindow.cpp b/qt-ui/mainwindow.cpp
index c24e2733e..acbd13046 100644
--- a/qt-ui/mainwindow.cpp
+++ b/qt-ui/mainwindow.cpp
@@ -57,6 +57,7 @@ MainWindow::MainWindow() : helpView(0)
 	connect(PreferencesDialog::instance(), SIGNAL(settingsChanged()), ui.InfoWidget, SLOT(updateDiveInfo()));
 	connect(PreferencesDialog::instance(), SIGNAL(settingsChanged()), ui.divePlanner, SLOT(settingsChanged()));
 	connect(PreferencesDialog::instance(), SIGNAL(settingsChanged()), ui.divePlannerWidget, SLOT(settingsChanged()));
+	connect(PreferencesDialog::instance(), SIGNAL(settingsChanged()), TankInfoModel::instance(), SLOT(update()));
 
 	ui.mainErrorMessage->hide();
 	initialUiSetup();
@@ -647,6 +648,7 @@ void MainWindow::readSettings()
 	GET_BOOL("gf_low_at_maxdepth", gf_low_at_maxdepth);
 	set_gf(prefs.gflow, prefs.gfhigh, prefs.gf_low_at_maxdepth);
 	GET_BOOL("show_sac", show_sac);
+	GET_BOOL("display_unused_tanks", display_unused_tanks);
 	s.endGroup();
 
 	s.beginGroup("GeneralSettings");
diff --git a/qt-ui/models.cpp b/qt-ui/models.cpp
index 4debafd9a..1e22f7da0 100644
--- a/qt-ui/models.cpp
+++ b/qt-ui/models.cpp
@@ -301,7 +301,8 @@ void CylindersModel::setDive(dive* d)
 		return;
 	rows = 0;
 	for(int i = 0; i < MAX_CYLINDERS; i++) {
-		if (!cylinder_none(&d->cylinder[i])) {
+		if (!cylinder_none(&d->cylinder[i]) &&
+		    (prefs.display_unused_tanks || d->cylinder[i].used)) {
 			rows = i+1;
 		}
 	}
diff --git a/qt-ui/models.h b/qt-ui/models.h
index 06dc66aa1..16818e407 100644
--- a/qt-ui/models.h
+++ b/qt-ui/models.h
@@ -47,6 +47,7 @@ public:
 	/*reimp*/ bool setData(const QModelIndex& index, const QVariant& value, int role = Qt::EditRole);
 	const QString& biggerString() const;
 	void clear();
+public slots:
 	void update();
 private:
 	int rows;
diff --git a/qt-ui/preferences.cpp b/qt-ui/preferences.cpp
index 382880a1f..67e2dfe8d 100644
--- a/qt-ui/preferences.cpp
+++ b/qt-ui/preferences.cpp
@@ -103,6 +103,7 @@ void PreferencesDialog::setUiFromPrefs()
 			ui.default_cylinder->setCurrentIndex(i);
 	}
 	ui.displayinvalid->setChecked(prefs.display_invalid_dives);
+	ui.display_unused_tanks->setChecked(prefs.display_unused_tanks);
 	ui.show_sac->setChecked(prefs.show_sac);
 	ui.vertical_speed_minutes->setChecked(prefs.units.vertical_speed_time == units::MINUTES);
 	ui.vertical_speed_seconds->setChecked(prefs.units.vertical_speed_time == units::SECONDS);
@@ -162,6 +163,7 @@ void PreferencesDialog::syncSettings()
 	s.setValue("gfhigh", ui.gfhigh->value());
 	SB("gf_low_at_maxdepth", ui.gf_low_at_maxdepth);
 	SB("show_sac", ui.show_sac);
+	SB("display_unused_tanks", ui.display_unused_tanks);
 	s.endGroup();
 
 	// Units
diff --git a/qt-ui/preferences.ui b/qt-ui/preferences.ui
index 283fbbb39..fb5a16abb 100644
--- a/qt-ui/preferences.ui
+++ b/qt-ui/preferences.ui
@@ -772,6 +772,17 @@
               </item>
              </layout>
             </item>
+            <item>
+             <layout class="QHBoxLayout" name="horizontalLayout_11c">
+              <item>
+               <widget class="QCheckBox" name="display_unused_tanks">
+                <property name="text">
+                 <string>unused tanks</string>
+                </property>
+               </widget>
+              </item>
+             </layout>
+            </item>
            </layout>
           </widget>
          </item>
diff --git a/subsurfacestartup.c b/subsurfacestartup.c
index 39da8e47c..0640333d0 100644
--- a/subsurfacestartup.c
+++ b/subsurfacestartup.c
@@ -29,6 +29,7 @@ struct preferences default_prefs = {
 	.font_size = 14.0,
 	.display_invalid_dives = FALSE,
 	.show_sac = FALSE,
+	.display_unused_tanks = FALSE
 };
 
 struct units *get_units()