diff --git a/Changes.txt b/Changes.txt
index 834d859e..fa88e586 100644
--- a/Changes.txt
+++ b/Changes.txt
@@ -1,22 +1,26 @@
 /**
 @page changes Changes
 
+## 0.3.1 January 9 2016
+
+- Improved performance 20-30% for large data files.
+
 
 ## 0.3.0 January 4 2016
 
 - Renamed `worksheet_set_row()` function to `worksheet_set_row_opt()` for
   consistency with current and future APIs. The `worksheet_set_row()` function
   is now used without the options parameter.
-  
+
   Note: This is a backward incompatible change.
-  
-  
+
+
 - Renamed `worksheet_set_column()` function to `worksheet_set_column_opt()`
   for consistency with current and future APIs. The `worksheet_set_column()`
   function is now used without the options parameter.
-  
+
   Note: This is a backward incompatible change.
-  
+
 
 ## 0.2.9 January 3 2016
 
diff --git a/include/xlsxwriter.h b/include/xlsxwriter.h
index e99718f6..88166579 100644
--- a/include/xlsxwriter.h
+++ b/include/xlsxwriter.h
@@ -18,6 +18,6 @@
 #include "xlsxwriter/format.h"
 #include "xlsxwriter/utility.h"
 
-#define LXW_VERSION "0.3.0"
+#define LXW_VERSION "0.3.1"
 
 #endif /* __LXW_XLSXWRITER_H__ */
diff --git a/include/xlsxwriter/xmlwriter.h b/include/xlsxwriter/xmlwriter.h
index 9947564f..449b0848 100644
--- a/include/xlsxwriter/xmlwriter.h
+++ b/include/xlsxwriter/xmlwriter.h
@@ -167,6 +167,8 @@ void lxw_xml_data_element(FILE * xmlfile,
 
 char *lxw_escape_control_characters(const char *string);
 
+char *lxw_escape_data(const char *data);
+
 /* *INDENT-OFF* */
 #ifdef __cplusplus
 }
diff --git a/libxlsxwriter.podspec b/libxlsxwriter.podspec
index 914ebf1d..9f08e6f0 100644
--- a/libxlsxwriter.podspec
+++ b/libxlsxwriter.podspec
@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name                  = "libxlsxwriter"
-  s.version               = "0.3.0"
+  s.version               = "0.3.1"
   s.summary               = "Libxlsxwriter: A C library for creating Excel XLSX files."
   s.ios.deployment_target = "6.0"
   s.osx.deployment_target = "10.8"
diff --git a/src/core.c b/src/core.c
index 55dc6ebf..f599d041 100644
--- a/src/core.c
+++ b/src/core.c
@@ -92,12 +92,12 @@ _write_cp_core_properties(lxw_core *self)
 
     LXW_INIT_ATTRIBUTES();
     LXW_PUSH_ATTRIBUTES_STR("xmlns:cp",
-                         "http://schemas.openxmlformats.org/package/2006/metadata/core-properties");
+                            "http://schemas.openxmlformats.org/package/2006/metadata/core-properties");
     LXW_PUSH_ATTRIBUTES_STR("xmlns:dc", "http://purl.org/dc/elements/1.1/");
     LXW_PUSH_ATTRIBUTES_STR("xmlns:dcterms", "http://purl.org/dc/terms/");
     LXW_PUSH_ATTRIBUTES_STR("xmlns:dcmitype", "http://purl.org/dc/dcmitype/");
     LXW_PUSH_ATTRIBUTES_STR("xmlns:xsi",
-                         "http://www.w3.org/2001/XMLSchema-instance");
+                            "http://www.w3.org/2001/XMLSchema-instance");
 
     lxw_xml_start_tag(self->file, "cp:coreProperties", &attributes);
 
diff --git a/src/styles.c b/src/styles.c
index 4b1022c8..fa3d46b6 100644
--- a/src/styles.c
+++ b/src/styles.c
@@ -89,7 +89,7 @@ _write_style_sheet(lxw_styles *self)
     struct xml_attribute *attribute;
     LXW_INIT_ATTRIBUTES();
     LXW_PUSH_ATTRIBUTES_STR("xmlns",
-                         "http://schemas.openxmlformats.org/spreadsheetml/2006/main");
+                            "http://schemas.openxmlformats.org/spreadsheetml/2006/main");
 
     lxw_xml_start_tag(self->file, "styleSheet", &attributes);
 
diff --git a/src/worksheet.c b/src/worksheet.c
index 94136b39..909bcb7a 100644
--- a/src/worksheet.c
+++ b/src/worksheet.c
@@ -2173,30 +2173,77 @@ _get_image_properties(lxw_image_options *image_options)
  ****************************************************************************/
 
 /*
- * Write out a number worksheet cell.
+ * Write out a number worksheet cell. Doesn't use the xml functions as an
+ * optimization in the inner cell writing loop.
  */
 STATIC void
-_write_number_cell(lxw_worksheet *self, lxw_cell *cell)
+_write_number_cell(lxw_worksheet *self, char *range,
+                   int32_t style_index, lxw_cell *cell)
 {
-    char data[ATTR_32];
-
-    lxw_snprintf(data, ATTR_32, "%.16g", cell->u.number);
-
-    lxw_xml_data_element(self->file, "v", data, NULL);
-
+    if (style_index)
+        fprintf(self->file,
+                "<c r=\"%s\" s=\"%d\"><v>%.16g</v></c>",
+                range, style_index, cell->u.number);
+    else
+        fprintf(self->file,
+                "<c r=\"%s\"><v>%.16g</v></c>", range, cell->u.number);
 }
 
 /*
- * Write out a string worksheet cell.
+ * Write out a string worksheet cell. Doesn't use the xml functions as an
+ * optimization in the inner cell writing loop.
  */
 STATIC void
-_write_string_cell(lxw_worksheet *self, lxw_cell *cell)
+_write_string_cell(lxw_worksheet *self, char *range,
+                   int32_t style_index, lxw_cell *cell)
 {
-    char data[ATTR_32];
+    if (style_index)
+        fprintf(self->file,
+                "<c r=\"%s\" s=\"%d\" t=\"s\"><v>%d</v></c>",
+                range, style_index, cell->u.string_id);
+    else
+        fprintf(self->file,
+                "<c r=\"%s\" t=\"s\"><v>%d</v></c>",
+                range, cell->u.string_id);
+}
 
-    lxw_snprintf(data, ATTR_32, "%d", cell->u.string_id);
+/*
+ * Write out an inline string. Doesn't use the xml functions as an
+ * optimization in the inner cell writing loop.
+ */
+STATIC void
+_write_inline_string_cell(lxw_worksheet *self, char *range,
+                          int32_t style_index, lxw_cell *cell)
+{
+    char *string = lxw_escape_data(cell->u.string);
 
-    lxw_xml_data_element(self->file, "v", data, NULL);
+    /* Add attribute to preserve leading or trailing whitespace. */
+    if (isspace((unsigned char) string[0])
+        || isspace((unsigned char) string[strlen(string) - 1])) {
+
+        if (style_index)
+            fprintf(self->file,
+                    "<c r=\"%s\" s=\"%d\" t=\"inlineStr\"><is>"
+                    "<t xml:space=\"preserve\">%s</t></is></c>",
+                    range, style_index, string);
+        else
+            fprintf(self->file,
+                    "<c r=\"%s\" t=\"inlineStr\"><is>"
+                    "<t xml:space=\"preserve\">%s</t></is></c>",
+                    range, string);
+    }
+    else {
+        if (style_index)
+            fprintf(self->file,
+                    "<c r=\"%s\" s=\"%d\" t=\"inlineStr\">"
+                    "<is><t>%s</t></is></c>", range, style_index, string);
+        else
+            fprintf(self->file,
+                    "<c r=\"%s\" t=\"inlineStr\">"
+                    "<is><t>%s</t></is></c>", range, string);
+    }
+
+    free(string);
 }
 
 /*
@@ -2235,30 +2282,6 @@ _write_array_formula_num_cell(lxw_worksheet *self, lxw_cell *cell)
     LXW_FREE_ATTRIBUTES();
 }
 
-/*
- * Write out an inline string.
- */
-STATIC void
-_write_inline_string_cell(lxw_worksheet *self, lxw_cell *cell)
-{
-    struct xml_attribute_list attributes;
-    struct xml_attribute *attribute;
-    char *string = cell->u.string;
-
-    LXW_INIT_ATTRIBUTES();
-
-    /* Add attribute to preserve leading or trailing whitespace. */
-    if (isspace((unsigned char) string[0])
-        || isspace((unsigned char) string[strlen(string) - 1]))
-        LXW_PUSH_ATTRIBUTES_STR("xml:space", "preserve");
-
-    lxw_xml_start_tag(self->file, "is", NULL);
-    lxw_xml_data_element(self->file, "t", string, &attributes);
-    lxw_xml_end_tag(self->file, "is");
-
-    LXW_FREE_ATTRIBUTES();
-}
-
 /*
  * Calculate the "spans" attribute of the <row> tag. This is an XLSX
  * optimization and isn't strictly required. However, it makes comparing
@@ -2308,44 +2331,44 @@ _write_cell(lxw_worksheet *self, lxw_cell *cell, lxw_format *row_format)
     char range[MAX_CELL_NAME_LENGTH] = { 0 };
     lxw_row_t row_num = cell->row_num;
     lxw_col_t col_num = cell->col_num;
-    int32_t index = 0;
+    int32_t style_index = 0;
 
     lxw_rowcol_to_cell(range, row_num, col_num);
 
+    if (cell->format) {
+        style_index = lxw_format_get_xf_index(cell->format);
+    }
+    else if (row_format) {
+        style_index = lxw_format_get_xf_index(row_format);
+    }
+    else if (col_num < self->col_formats_max && self->col_formats[col_num]) {
+        style_index = lxw_format_get_xf_index(self->col_formats[col_num]);
+    }
+
+    /* Unrolled optimization for most commonly written cell types. */
+    if (cell->type == NUMBER_CELL) {
+        _write_number_cell(self, range, style_index, cell);
+        return;
+    }
+
+    if (cell->type == STRING_CELL) {
+        _write_string_cell(self, range, style_index, cell);
+        return;
+    }
+
+    if (cell->type == INLINE_STRING_CELL) {
+        _write_inline_string_cell(self, range, style_index, cell);
+        return;
+    }
+
+    /* For other cell types use the general functions. */
     LXW_INIT_ATTRIBUTES();
     LXW_PUSH_ATTRIBUTES_STR("r", range);
 
-    if (cell->format) {
-        index = lxw_format_get_xf_index(cell->format);
-    }
-    else if (row_format) {
-        index = lxw_format_get_xf_index(row_format);
-    }
-    else if (col_num < self->col_formats_max && self->col_formats[col_num]) {
-        index = lxw_format_get_xf_index(self->col_formats[col_num]);
-    }
+    if (style_index)
+        LXW_PUSH_ATTRIBUTES_INT("s", style_index);
 
-    if (index)
-        LXW_PUSH_ATTRIBUTES_INT("s", index);
-
-    if (cell->type == NUMBER_CELL) {
-        lxw_xml_start_tag(self->file, "c", &attributes);
-        _write_number_cell(self, cell);
-        lxw_xml_end_tag(self->file, "c");
-    }
-    else if (cell->type == STRING_CELL) {
-        LXW_PUSH_ATTRIBUTES_STR("t", "s");
-        lxw_xml_start_tag(self->file, "c", &attributes);
-        _write_string_cell(self, cell);
-        lxw_xml_end_tag(self->file, "c");
-    }
-    else if (cell->type == INLINE_STRING_CELL) {
-        LXW_PUSH_ATTRIBUTES_STR("t", "inlineStr");
-        lxw_xml_start_tag(self->file, "c", &attributes);
-        _write_inline_string_cell(self, cell);
-        lxw_xml_end_tag(self->file, "c");
-    }
-    else if (cell->type == FORMULA_CELL) {
+    if (cell->type == FORMULA_CELL) {
         lxw_xml_start_tag(self->file, "c", &attributes);
         _write_formula_num_cell(self, cell);
         lxw_xml_end_tag(self->file, "c");
diff --git a/src/xmlwriter.c b/src/xmlwriter.c
index 70cdafbc..e244fe0c 100644
--- a/src/xmlwriter.c
+++ b/src/xmlwriter.c
@@ -18,7 +18,7 @@
 /* Forward declarations. */
 char *_escape_attributes(struct xml_attribute *attribute);
 
-char *_escape_data(const char *data);
+char *lxw_escape_data(const char *data);
 
 void _fprint_escaped_attributes(FILE * xmlfile,
                                 struct xml_attribute_list *attributes);
@@ -180,7 +180,7 @@ _escape_attributes(struct xml_attribute *attribute)
  * in that double quotes are not escaped by Excel.
  */
 char *
-_escape_data(const char *data)
+lxw_escape_data(const char *data)
 {
     size_t encoded_len = (strlen(data) * 5 + 1);
 
@@ -305,7 +305,7 @@ _fprint_escaped_data(FILE * xmlfile, const char *data)
         fprintf(xmlfile, "%s", data);
     }
     else {
-        char *encoded = _escape_data(data);
+        char *encoded = lxw_escape_data(data);
         if (encoded) {
             fprintf(xmlfile, "%s", encoded);
             free(encoded);